HELP! possible virus or spyware

I need some advise on how to fix my computer.
I am having problems with my computer running slow.
programs will not run or will just close and will not
start again until I restart my computer. Internet
explorer will not run at all. my cpu is at 100% and the
commit charge is running at 1500M the page file usage is
at 1.5GB. to get on the internet I have to close
EXPLORE.EXE in the task manager. my virus scan continualy
becomes disabled.
I have kazza and I am trying to delete all files related
to it.
I can download updates from microsoft but cannot install
them. I don't know why
I am so frustrated I'm about to do another system
restore but I don't know if this will fix anything.
I have an HP pavilion 503n
windows XP
384MB ram
intel celron 1.7ghz
mcafee fire wall
mcaffee virus scan (updated)
spybot
ad aware
Any help will be greatly appreciated