My PC keeps rebooting unexpectedly - apologies, you 've had this quite a lot before!

CPU is a Pentium 4 2.8ghz EM64T
MOBO is an MSI Intel 915PL Neo
RAM is DDR 266, 2 x 256MB - wrong FSB I know - new stuff on the way!
GPU is an ATI Radeon X550 on a Connect 3D card (256MB onboard)
PSU came with the case and is a 480W Colors IT one
OS is XP x64 build 3790 with SP1

Its rebooted 3 times - once in FIFA 2005, once when I was installing Nero and once just from the desktop with no activity. No BSOD as yet - just a system error in Event Viewer - minidump from the last incident attached. Error code for the last one was 0xC2. No graphical issues in games etc - all working well. The only thing to note is that I had to manually install the driver for the video card as the x64 version of the Catalyst drivers didn't pick up the card automatically. Many thanks for any help anyone can give!