slowdown?

I wonder if any of you guys have encountered what im about to say, now i know all the stuff about system processes right and how to slow them down thier priority if needed. But i wanna know if their are programs that we use day to ay out there that may slow down our system performance. ive heard certain configurations cause major slowdowns, even theway you install programs e.g windows updates then codecs, or codecs then windows updates, if they are installed a certain way, they sometimes tend not to agree wit each other. I have had a problem lately with things such as winrar and winzip especially, in them taking almost 20 minutes to unzip, where as before they would take less then 5. Keep i nmind i have apowerfull system of p4 3.0 ghz 1gb ddr 128mb 8x agp graphics card with hyper threading technology, and in the beggining everything was wroking fine, now everything is just slow for me, i wonder what it could be. If you guys have any ideas, such as maybe norton antivirus, certain spyware programs eg. i have spybot and spy sweeper running all the time alongside norton...whatever it is can you guys please give a crack at it...holla back