Thanks to the generous help of some friends, I was able to finish building my amd64 machine. Here are the specs:

• CPU: AMD Athon64 3000+ Venice Socket 939 ($146)
• Mobo: MSI K8N Neo4 with nVidia nforce 4 chipset and onboard audio/LAN/PCI-E ($90)
• HDD: Hitachi Deskstar 164.7GB SATA 7200 RPM ($90)
• DVD: LG GWA-4131B DVD-RW drive ($65)
• Kingston 512MB DDR400 RAM ($38)
• Graphics: nVidia GeForce FX 5200 PCI (lifted from an older computer) ($70)

I need a floppy disk drive, a surge protector, a monitor (duh), and a wireless router.

Already got this stuff. $10 for the surge protector, the monitor and floppy drive were free because I got them from a friend, $25 for the router.