I'm having an issue with an older laptop and i'm not sure what or where the cause of the issue is.

What seems to be happening is that whatever process is currently running, it uses up 100% of the cpu utilization. It's very very odd. At first, it was Security essentials causing the issue, then it was windows update. Loading process viewer causes a constant 20% CPU utilization right there. What seems really odd to me, is that the computer has had XP re-installed from scratch 3 times so far over this issue and it's finally hit my desk.

Culprits i've seen at 100% usage:
security essentials
Norton AV
Iexplorer
Explorer

It's a clean install, fully updated and never been on the net except for windows update.

This problem also occures in safe mode, though not as bad.
CPUid shows proper clock speed for the processor, though it is an older Celeron M 430 processor (1.8 gig)


any ideas?