I've built a couple dozen PCs over the years for friends & Family, but I'm finally going to build myself a Quad-Core!! (my first Quad build)

When my friend upgraded his system, I bought his old
Phenom X4 9950 Black AM2+ 2.6ghz

I'd like to run W7, 64-bit. Is that possible?

I currently have 2gig RAm and plan to go to 4gig. Is it really beneficial to go any higher?

I currently have a Saphire Radeon x800 Pro, PCI-E. I'll probably update later, but don't see going to SLI.

Can anyone recommend a good mobo for under $100?