Vista is shit, everything run slower, it rapes your HDDs, heaps of software isnt compatible, heaps of hardware isnt either, it has massive bugs (like loosing control pannel and desktop settings)
oh, and just like XP it suffers from the memory hole issue, so the only real way to get more than 3gb of ram is to goto 64bit windows
vista home basic (VHB) = no areo gui, can play dvds, basic networking
vista home premium (VHP) = areo gui, can play dvds, basic networking
vista business (VB) = areo gui, no native dvd playback, advanced networking
vista ultimate (VU) = the works (its got it all)
but sounds too much like a holden gathering for me.... stick with XP and its alll good!! =)
if you want me to explain the memory hole i can... its a bit f**ked up, but im sure you will get the idea (or lack of =P)
as far as getting a gamin PC, get the fastest possible graphics card you can afford (either 8800gts 320 or 8600gts), ram speed is irelivant provided its 667 or better (CAS latency = no performance differance on a core2 or amd) try for 2, but 1 gig with XP is fine, if you can afford a core 2 duo get one, if not AMDs cpus are good for what you pay for em these days, dont skimp on PSU (but avoid antec smart power range)
ruf prices would be something like E6320 $280 + gigabyte mobo $230 + 1gb corsair 130 + 8600gt $330 + antec case/psu $190 = $1160 (im sure people could point you to cheaper prices... hence why its ruf =P)