Here is what I would get if I were u,

AMD Athlon 64 3200+ or higher
Shuttle AN50R nForce3 motherboard
1GB of ram such as corsair at leat pc3200
ATI Radeon 9800 pro or XT
two SATA maxtor hard drives and put them in RAID 0 using the onboard RAID controller found on the mobo
Make sure ur case has a lot of power in the PSU. I would stick above 400W

currently the lowest prices are at

www.zipzoomfly.com
www.newegg.com
www.excaliberpc.com

Oh yeah if u want something sleek go to excaliber and look at their Shuttle XPC system for AMD 64. It is the shit. Built one for my boss and it is just as capable but really small and sexy. If u bught that then all u would need is a cpu, ram, gfx, and hard drive. Really easy to build