If its AMD the choice starts here!!!!!
**AMD 64 X2 4400+@dun know(Extreme perf with 2x1mb cache)
**AMD 64 X2 3800+@13~14k (costly it might seem, but defenitely worth it 2x512kb)
**AMD 64 3500+ @9.5~10k (extreme perfomance in overall single threaded apps and good compared to dual cores in multithreaded apps)
**AMD 64 3200+@7k (Good perfomance and very good value for money and has potential to oc to hogh values)
**A8NE @ ~5.5k (Very good mobo with tons of everclocking options and rock solid with nf4 ultra)
**A8N SLI Deluxe@8k (SLi ready, highly ocable, great value SLI mobo,nf4SLI)
**MSI K8N Diamond@8~9k(SLI ready, ocable, creative 24bit 7.1 onboard audio, tons of features, nf4SLI)
----------------------------------------------------------------------
All of these are 64 bit and vista compatible. If u add a GF7 series card u can enjoy the transperencies and other visuals in Vista (At least a FG7300@5k)
All of these mobos(and proc) supports only DDR1 (but at ultra low latencies) but could produce higher memory bamdwidth scores than DDR2 on Intel if u use quality rams with low latencies and good mobos(above ones).
------------------------------------------------------------------
For the mentioned price ur best choice(if AMD) would be a 3200+9 with an A8N E mobo.