I have put up a dedicated mining computer now, and I'm having a lot of problems with it, but I'll take one at a time. I am running GUIMiner
I'm getting this error message:

2013-05-11 16:26:06: Listener for "OpenCL Slush's": stratum.bitcoin.cz:3333 11/05/2013 16:26:06, Verification failed, check hardware! (0:0:Juniper, 2b5342eb)

when I am running an OpenCL miner connected to your pool.

You have said to others having this problem that it is most likely hardware or driver error, but I can run Phoenix (with BitcoinPool.com) without problems. What could it be? I have tried different flags.

PS: I tried running an OpenCL miner on BitcoinPool.com and I get the same problem:

2013-05-11 16:38:50: Listener for "OCL BCPool": bitcoinpool.com:8334 11/05/2013 16:38:50, Verification failed, check hardware! (0:0:Juniper, 74f69135)

I could try the other graphics card (that has other drivers), but please don't ask me to do it today... I have spent at least 6 hours and 20 reboots on trying to get the graphics cards working as I want, but they still don't. Nothing seems to work the way I want it to today.