@Milkshanks It says a file is missing, so guiminer might have been installed into a folder with strict permissions, such as Program Files. He should try installing into a normal data folder, not a system folder.

On a side note, I'd appreciate if guiminer could be made to install in Program Files and the 'Programs and Features' Control Panel with a normal setup program, this is the only application I am running that does not conform to Windows requirements or guidelines.

Eventually all antivirus will report and delete Ufasoft bitcoin-miner.exe, I hope it's removed or replaced by another CPU miner in the next version of guiminer, since nobody uses CPUs for mining any more.
I don't know if it's linked, but I haven't been able to get rid of this unwanted 50% CPU usage since the new version and since my antivirus BitDefender has removed this executable. Together with the GPU usage, it has been killing my machine right and left, with shutdowns caused by high temperature and even a couple of blue screens (never had any for the past 5 years.)

So I'm probably looking at mining using phoenix directly or some other GUI miner. I have stopped mining altogether because of the 50% CPU usage on one core thing. I do NOT want guiminer to use my CPU for mining.

Ironically the GUI of guiminer.exe (2011-07-01) disappeared from my Windows 7 x64 machine.
After investigating, I found out that poclbm.ini's settings for "window_position" were changed to -32000 for both horizontal and vertical positions. I reset them to 0 and I could see the GUI again when launching guiminer.exe. Hope this helps other people. You may want to check why it resets to -32000 instead of 0. It happened a second time to me just now, while I was opening and closing guiminer.exe to test it. Here's the ini content:

    "window_position": [
         -32000,
        -32000,
        160,
        27
    ]

Also, I noticed that the poclbm.exe process is now taking up 50% of the CPU usage, with the first of the 2 dual core CPUs at 100%, when it used to be 0% with the 2011-06-09 version of guiminer.exe. I saw that "CPU Affinity" had the #0 CPU checked, so I unchecked it, but all it did was switch the 100% usage from CPU #0 to #1 in Windows Task Manager.
There is just one miner in guiminer.exe, the default one using the NVidia card. Both CPU Affinity checkboxes are unselected, there is nothing in the Extra flags box. So it looks like mining happens both on the GPU and the CPU, with a slightly lower MH/s rate compared to when it mined on the GPU only.

Strangely, both bugs appeared at the time BitDefender reported a Trojan in guiminer\miners\ufasoft\bitcoin-miner.exe and deleted the file. I also inadvertently launched a second guiminer.exe process at about the same time (because the first one was not visible in the Notification area by default) which apparently resulted in 2 guiminer processes running each half the MH/s rate than the previous unique process used to run, and I haven't been able to run guiminer normally every since, even after reinstalling with BitDefender disabled.

There is no trace of guiminer or poclbm in my Registry, I cleaned up the Notification Area Icons, deleted and redownloaded guiminer, so I don't know what's happening and how to get back to 0% CPU usage.

But that's still putting all this money into a single basket, bitcoins. It does not matter if it's stored in different wallets, it's the same currency. If the exchange rate collapses or something happens to the currency, you have 25,000 BTC valued at $0.

I invest all of the $ salary that I don't spend, I invest into other areas half of the $ earnings I get from trading, it's a common sense security against something going wrong. Even if you lose all your earnings or they got stolen, you still have whatever you invested into these other areas, which with time represents the majority of your capital.

It's a good first step, but it's still putting all your eggs in the same basket. You need to diversify. Even if you want to keep bitcoins as an investment or to promote the system, you need to invest at least one out of each two bitcoins mined into a different portfolio. Be it gold, real estate, remunerated savings account, stocks, venture capitalism, more mining rigs, take your pick. And don't forget to give 10% to charities!  

You do know that there is no motherboard that can fit 7 PCI-E x16 cards, right?
Or that most decent 5770 are double slots?
Or no PSU powerful enough or probably no circuit breaker and outlet in your house powerful enough to feed that monster?

Been mining for a few days only, since the recent media articles on bitcoin.
My Nvidia 8800GTX was the shit 4 years ago, at $500-600, but it mines at only 26 MH/s, miner software are optimized only for Radeon's stream processors, not Nvidia CUDA.

I was planning to build a new PC later this year, might as well do it now, using Radeon cards this time.
I'd love to use 2-3 6990s but they are out of stock, so I'll aim for 1 GH/s instead of 2.

It's called a pool, but there's probably no point for the casual miner at this stage.
OK, you may get 1 BTC a day for free if you're lucky, probably more like 1 BTC a week very shortly because of the mining competition increase, but it probably makes more sense to buy 1000 bitcoins at $10 each and resell them when they reach $20/BTC.

That's assuming the exchange rate will increase, which is likely in the medium term, but now the American government is looking at the bitcoin system, so I would not keep bitcoins on the long term. I know, "they'll never be able to shut us down etc."

If you make enough money buying and selling bitcoins to pay for a mining machine, like a $3000 PC with 3 Radeon 6990 cards that mines at 2 gigahashes/second, or even a less ambitious system, then it's a different matter, because you basically got it for free and can resell it for real money if you need to. Just don't expect a mining machine bought now to pay for itself any time soon. Still, for the gamer, you get a great machine at reduced price.

A picture and motherboard brand & model would help. Is it a EATX motherboard?
If you can't fit the fourth card physically because the graphic cards are double-width, there's not much you can do if you want something integrated with your air cooling system.
Unless it could fit with some cuttings in the back panel or something, or replace the motherboard or computer case with one that supports 4 cards.
You can also replace the single cards with dual ones, like the Radeon 6990 (that's out of stock.)
Check hardware or overclockers forums such as hardocp or the hardware section in this forum.

Introduce myself? So you can identify me from my typing pattern and link it to my bitcoin address? I don't think so! 

I'm confused, you now say he paid more, but you said he paid 50% of one rig in your first post.
The only fair distribution is that he gets his share only from the rig he participated in paying for, not the other one you paid fully yourself.
If he paid 60% of the other rig, he gets 60% of the bitcoins mined by that rig (use a different pool if it makes computations easier) minus 60% of the electricity cost of that rig (assuming you're the one paying the bill.) Buy a Kill-A-Watt to check how much power the rig uses.
If the rig is responsible for 10% of your home, electricity cost is 10% of the fixed bill plus 10% of every KW range.
You probably need to do the computation only once, and set his electricity bill as a fixed charge.
You can both decide whether his electricity bill is either paid in cash or deduced from his mining rewards at the current change rate at the end of each period.

You obviously need his approval for this change, since you already agreed on 25% of both rigs' mining.

Thanks, @petercyr, I knew there'd be such a chart somewhere!
Wow, it looks like the miner apps are not optimizing CUDA at all, just for Stream.
Top of the line Nvidia GPUs have similar or better performance than Radeon for gaming, yet 4 times less for mining.
I guess my new machine will be a Radeon 6xxx series...

I have a 8800 (GTX) like nickman, but it connects fine.
I was wondering however if a 26MH/s rate was normal for this video card, when I see recent cards going at 400MH/s.
A bit off-topic, but is there a reference chart listing the MH/s rate for different GPUs?

It does not look like guiminer is actually using the card at all, there's no CPU/memory usage, as expected for a GPU app, but there's also no more heat than usual (the GPU fan usually starts rotating faster and making more noise if the GPU is heavily used.)
Is there a way to increase the GPU usage in guiminer? I couldn't find any setting in the UI.
I thought maybe the default miner was wrong, so I created a second CUDA miner, but it only went from 26MH/s for the unique default miner to 1MH/s for default and 25MH/s for CUDA.

Is there a help site to learn more about guiminer, aside from this (long) thread? Like all the switches that are mentioned here.
And another noob question: I am not using a dedicated mining machine, it's my main desktop machine, but I noticed the MH/s rate is the same when I am not using the machine. It would be great to max out the GPU automatically when the computer is idle.

I am just getting started on the whole bitcoin thing, so I appreciate a lot the GUI approach.
It might benefit from a little more UI simplification or integrated help for the bitcoin newcomers.
For instance, a real setup. Guiminer currently does not run if you copy the folder to Program Files because of the Windows permissions. It's also not listed in Add/Remove Programs Control Panel.
Solo mining is unnecessarily complex too, it should probably launch the bitcoin client as server automatically, as it's not clear it's a required step. Not even sure why a password is required for solo mining.
Sorry, I know it's done on your own time, I am not making requests, it's just directions if you intend to go that way.
I have installed the latest version, so I don't know how updates work, if they are automated or not, but I suggest to track the MH/s rate before and after the updates, to offer a revert to previous version option in case the update affects negatively the MH/s rate. That'd be cool!

Now on to some GPU hunt...