Ugh...1GB of VRAM? I can't even theorycraft where that would put you. Two accounts maybe? The modern clients take up (in my experience) 1.3-1.8GB of system RAM each. So with OS overhead, you'll probably be limited to two regardless of the video card support. 3 might "work" but I wouldn't expect it to be something I'd call "fun."

[edit] Do some reading around here on the other performance/build threads. Folks are struggling to box 5 in BofA with 8GB of system RAM and much more capable video cards.