Pc Performance, Tips and tricks for speeding up PC Performance

I think we need a thread to discuss tips/tricks for PC Performance.

Other than virus/spyware scans and adding more memory, what have you found to increase system performance on windows 2000 and XP systems?

I have found a couple of things to provide a temporary fix, but, unfortunately, I don't know enough about the OSs to tell you why these fixes work.

Some of the things that have worked for me:

Get rid of seldom used programs. This is easy enough to do through the "add/remove programs" menu.

Defrag, clean out temp files, and do just about everything else you find in Start -> Programs(or All Programs) -> Accessories -> System tools

Reset some of the services on your machine to a startup type of "manual" rather than Automatic. Do this by going to Start -> Run -> services.msc.
Be carefull what you change. Google it first. You can reset some of the TSRs by going to the program itself and setting some flags in the application rather than in serices.msc. A couple of examples are Outlook and Messenger. You can reset both of these applications to not start automatically for a barely noticable gain in performance.

Before making changes you are unsure of, be sure to google or post to the forum for advice. Also, it's always a good idea to have a current backup of your system state as well as any data you have on your HD.