Please dont laugh too hard...
But my Gfx card is an Nvidia Gtx 260 and my CPU is an Intel Core 2 Quad Q6600
Ouch. Yeah, that's a little out of date. I can't find any benchmarks on Monero for the 260; I did find someone saying he's receiving 32.5 MH/s on Ethereum mining with a GTX 290, which seems great considering the rates more powerful graphics cards are getting. That's roughly the same hashrate I found on an old benchmark chart showing GPU efficiency in Bitcoin mining for the 260. Obviously 30 MH/s wouldn't be worth the power it costs with the current Bitcoin difficulty, but if it can really pull 20+ MH/s on Ethereum that's fairly solid, enough to mine 1.75 ETH a year at the current difficulty. The 260's reasonably low on electric costs at ~180 watts, which would put your profits at about $4-500 a year. If it performs similarly well with Monero, at a 500+ H/s rate and that power draw it would be about the same profit rate. Depends if those hashrates are accurate or not though, I'm curious if they are.
Ok, a few questions spring to mind from you post.
1) GUIMiner tells me my GTX 260 cant be used to mine with?
2) Which mining software would you recommend for casual/hobby mining of Eth/Mon on my GTX 260
3) I see lots of different variations of ETH... which is still GPU mining on a home PC?