constant cpu usage from phantom process/system overhead

[Keego]

Hey, I don't know what's going on here, but a friend has a HP pavilion ZE4100 (Celeron) with XP Home running on it and task manager says that the system idle process is at 80-96% but the performance graph AND the perfmon reports that it's running at an average load of 52%. WTF? No programs are running and I disabled nav's real time scan and it doesn't have any affect.

Any suggestions to find out exactly what is taking up the cpu usage? It's causing the system fan to kick in 100% of the time