Futher too my first question about slow sticking PC?

Please Read my other question and answer it there if you can.

My lap top was designed to run Windows XP it has the Windows logo label on it. My memory is 195952K. Cached memory is around 40000k and it say available memory around 44,500 these to figures dont add up to the total. Where is the other 11,000k or so gone? I have a 80Gig hardrive in it with just over 70Gig free on the disk so it isnt full up. All though the CPU usage rarely rises above 7 percent in normal running it does Spike at regular intervals but never reaching 100% and only for a split second. Its the high PF usage which never used to be there. and the High Paged Faults that has me wondering why? What causes high Paged Faults?

I have run registory clear up on it aswell. I have checked the start up programs and stopped the one i dont really need from starting up. Could a downloaded program/virus get passed a system restore. When I roll back to a previous system restore point?

Thanks for answering