CPU usage spiking, help!

My CPU usage is spiking a lot lately since I reinstalled my Windows XP, I'm running an X2 4400+ on ASUS A8N-SLI, nothing's overheating and voltages look fine. Most of the time I'm only playing some movies in the background as I do homework, so normal CPU usage is about 10%, but now it spikes to 100% periodically and it's becoming more frequent. I'm sensing that there's something wrong but I'm unable to pinpoint it. Please help!

i have'nt got the foggest idea if this will help,but have you installed the dual-core optimizer?may want to check for updated board drivers to.

Are you keeping any web pages open in the background as well?

Some flash ads can spike CPU usage (like some of the recent newegg ads here as reported in the Help/Feedback forum).

is the advertisement thing at the top of AIM 6.5 flash based? cuz it looks like the spikes is related to my AIM and windows live messenger. I was able to stay spike-free for almost an hour without them but as soon as I turned them back on, I started getting spikes again.

I had the dual-core optimizer before I reinstalled, it didn't seem to do anything so I didn't bother to get it again this time, but I'll install it later.

check in task manager or get processor mon.

I would recommend that you check your Index Service under administrative tools>services. I had a simular symptom when I installed microsoft desktop and then removed it. Until I set the index service to manual (from automatic), my cpu usage was at 100% even when my usage was minimal.

If it is not that, you may have a spyware problem, especially if you have a lot of popup when you turn on your computer.