Computer seizes up

My computer just seizes up every couple of seconds, like when I am scrolling,
it will stop scrolling for 20ms, then jerk down to where the mouse is. It gets kind of annoying while tring to play games, because it jerks every 3 seconds...
Any kind of help would be appreciated.
I have a WinXP Pro(Gateway.) P4 2GHZ 256 MB RAM and 2 40GB hard drives... One seagate and one western digital.
Usually, when I have computer problems, I just reinstall windows, and I don't really want to do that... Dont AVG antivirus, no viruses showed, Spybot S&D, defragged, turned off all unneeded services, removed all unknown registry bloat, run Ad-Aware, and removed all programs I didn't need.
It still does it!!!!
I am really angry at my computer right now... :'(

Any help would be VERY appreciated...

Karvec

 

Does it happen in Safe Mode?

 

No, it doesn't happen in safe mode, as far as I can tell.

 

Try disablitn startup items in msconfig, and third party services in the same place.

There is a checkbox on the services tab that says hide all MS services.

 

I did that, then did a complete reinstall after that didn't work. It still does it. I recently got a DSL connection, could that be the cause? It is an Elastic Networks DSL modem, and it is connected to an onboard LAN connection. Or should I post this in hardware?

 

What is your memory usage? My Compaq came with 256 MB memory and when I played games or opened a lot of windows, it bogged down like your's is doing. Check your memory usage in your Task Mgr., if you are utilizing all 256MB and working off the Paging File on the HD, you might want to consider more memory. 512MB seems to be the minimum recommended amount, more for serious gaming and graphics apps.