My first SLI attempt

Of course you will be able to run crysis at max, assuming you are willing to play at 1024x768. Crysis at max is an incredibly expensive and stupid way to choose your GPU, even the latest 5870 can barely run crysis on ultra high while getting better than 40FPS at 1680x1050. We need to know your monitor resolution to be able to tell you what level you will be able to play at.
http://www.tomshardware.com/review [...] 22-13.html

You can use XP, but you can get vista home for $110 off newegg with an upgrade coupon to windows 7, thats the method i would suggest, windows 7 is much nicer than XP and can do far more, especially with DX10 and DX11 support.

well, if you are doing sli, i am assuming you are getting two of those GTX260's

for that price you are better off getting one ATI Radeon HD5870 (and being able to crossfire later)

i dont really like Crossfire tho..... I dont know your going to have to convince me XD

Crossfire and SLI are very similar, on a hardware level crossfire is more advanced. That said they are both basically the same when it comes to scaling and performance. Also, while they usually take longer to come out, ATI's drivers tend to have fewer problems than nVidia's since nVidia just produces copious amounts drivers at a whim. Again, that said they tend to be equal. The largest difference between ATI and nVidia are the extras. With nVidia you get Physx, which is 100% useless, and CUDA, which helps with slower processors, but your i5 will do fine without it. With ATI you get Eyefinity (5XXX series), which is basically the most advanced multi-monitor process out there but again it has limited uses. With ATI you also get Havoc, instead of Physx, which again is basically useless. Finally, when going to ATI route, you get not only DX 10.1 support (4xxx series), but now you get DX11 with the 5xxx series. That will allow you to stay up to date for years and will allow you to play any game that is produced in the near future. Note that when DX11 is enabled in a mainly DX10 game it will add a performance between 20%-50% over any non DX11 card. In DX11 based games it will, of course, do far better even if the game has a DX10 mode, as long as it is based on DX11.