Computer gets to WinXP Pro boot, then restarts - sometimes

[337]

I've been having this issue since I put together my computer. The computer gets to the WinXP loading screen, the white progress bar stops, and then it reboots. It'll do this between 0-4 times (sometimes it just loads right up). any ideas?

Computer Specs:

AMD64 3200 939 Venice
Asus A8N-SLI Deluxe
EVGA 6800GS
Antec NeoHE 500 (recently replaced for new version due to compatibility issues with mobo)
Antec P180
Hitachi Desktar 160GB HD
Kingston PC3200 1GB dual channel (2x512)