thulium

I'm not a techie and don't have the time to keep up with most of the advances, so most of the articles and reviews I read is for specific problems or 'is this better than that.' My problem at the moment is I'm attempting to put together a gaming machine for my grandson that can also be used for high end Photoshop applications. I'm trying to decide if I want to go with a single GSU (the newer 2900) or PSI (two 8800 GSUs) and which Mobo to use. I've read reviews on Mobos based on the nForce4 chip set and also the 480.One said the 480 could only run in x8 x8 mode for SLI. Another article referenced a RD580 chipset that can run in x16 x16 mode for PSI. That particular article was for an AMD system so it may be that the RD580 was for AMD only?? Is either the 480 or nForce4 better for SLI than the other and which Mobo might one look at that has it? I'll probably be using WIn 64 Pro with 4 gigs of DDR2..........thanks