1. go into msconfig/startup and look carefully at each item checked. After doing some research, you will find that most can be unchecked.
2. look carefully at each icon to the left of the time on the bottom taskbar and see which ones don't need to be running.
3. look carefully at control panel/add or remove programs and see which programs you never use and can be removed from your machine. You can find a list of entries and explanations here: http://www.sysinfo.org/startuplist.php
4. do disk cleanup and disk defrag
5. do a complete scan with your antivirus
6. download spybot and do a complete scan. Then remove the program. Redownload it each time you want to scan your computer. don't need it hogging resources or even sitting there.
7. my computer guy recommends the same procedure for malware and Steve Bass (who you should subscribe to) recommends the same. read about it here: CCleaner: http://www.techbite.com/newsletter/2/have-a-slow-system-try-these-f...
and there's other things to do, too, but start here!