A few suggestions:
- try running Spybot (it's software you install). It may clear some things out that McAfee isn't aware of.
- clean up your start-up programs (
http://windows.about.com/od/customiz...t_programs.htm)
- defrag your drive
- get more RAM (how much do you have now?)
- last resort: reinstall windows. You have to back everything up first though!