Symptoms: System starts normally, and after a few seconds task manager shows the CPU go to 100%. From there it will never go down. No specific process is using the CPU, this is all kernel time.
Of course, the PC becomes nonresponsive and after a while (usually less than 30min) it just freezes and a hard reset becomes the only alternative.
This is after a fresh XP install from the CD and then installing the SP2 from Windows Update. Nothing else installed (but my NIC drivers from my Mobo original CDs)
Mobo: Asus A7N8X-XE (BIOS up-to-date)
Mem: 512MB on A1
CPU: AMD Sempron 2500+
GC: Asus V9520
Else: 1 UDMA HDD, 2 UDMA CD/DVD/RW