>>You mean in msconfig keep Avast, zonealarm and one of the spyware programs [AVG or SuperAntispyware], right?
I don't know if this will help or not but I would clean it out. 2 years...it is do for a cleaning. A P4 will slow down if it starts to overheat. Dust can cause it to overheat. You'll have to click the 'x' to clear the ad:
How much RAM do you have?
I have 512 MB of RAM.