This thread is good as I had not heard of Process Monitor before.
My laptop with Vista 64 is doing something weird now as well when unplugged.
The processor utilization is always very very low. Idle is 99% but when I try to open programs or folders it sometimes seems to hang for a bit first. It could just be a slow hdd though I guess, but I have used slow hdd before and they never seemed this bad. I wondered if something was wrong with power management as the computer actually can run very fast when plugged in at least.
I suppose I should have got an ASUS laptop instead of HP as ASUS are known for having crappy/nonexistant power management. Thus their batteries don't last but they have blistering performance.