1) Start->Run->msconfig
2) Go to "Startup" tab and turn off any programs you don't need or don't know what the hell they do (use trial and error to see if you DO need them).
3) Start->Control Panel->Administrative Services->Services
4) Disable (or set on "Manual") any services you don't use ("Messenger", which is NOT Windows Messenger, FTP, and Telnet are all excellent choices and will increase your computer security)
5) Run a Scandisk (called "Checkdisk" in Windows XP) then Defrag by selecting Properties on your Hardrive and going to the "Tools" tab (top option is CheckDisk, bottom is Defrag).
Now less common solutions, but they MAY still work...
6) Make sure you have at least 600MB of free space for virtual memory. Remember you can delete your Temporary Internet Files and Temp files by going to Start->All Programs->Accessories->System Tools->Disk Cleanup. The more HDD space you have, the more space is accessibly for virtual paging.
7) Uninstall any programs you aren't using.
8) Increase the RAM in your computer. For Windows XP, you should have at least 256MB of RAM, while 384MB is recommended. If you already have over 384MB, then upgrade it further as whatever your environment is, it seems you need more memory to keep up.
9) Upgrade your processor. This will provide a sizable boost in performance if you're running a 1.5GHz Pentium 4 / Athlon XP or lower. If you're running a Celeron or Duron, then you'll need 3.0GHz for the same performance
Note that you should look at adding more RAM FIRST.
10) If you have a virus scanner, try to make it "less active". All virus scanners I know of have this option, and it makes the scanner less paranoid as it does not check EVERY single file EVERYTIME it is accessed.
When I think of anything else, I'll let you know.
