Yeh need 1.5-2 gigs just to run vista unless yeh disable that nifty gui and what not. Then if yeh do that there aint really a good reason to run vista.

If yeh got 4 gigs I would suggest Xp
If yeh wanna run vista go with the 64bit version and get 8 gigs

I agree with yeh Nitro but yeh can reduce how much memory the graphics cards eat up by changing the bios setting.

with that box yeh should be able to run a 5box with ease even if yeh run vista with cycles to spare.