I can't yet post links in the forums, but here is something that may help:
1.) Go to Google.
2.) Do a search for "Game Booster"
3.) The second link should read "Game Booster - Free software downloads and software reviews - CNET"
It is entirely free to use and it contains no spyware or viruses. Basically, it temporarily shuts down services that aren't necessary for playing games. This slightly frees up your system resources.
Another thing to try would be to clean up your temporary files.
1.) Click on your Start button.
2.) "Programs"
3.) "Accessories"
4.) "System Tools"
5.) Disk Clean-up
6.) Select your C:/ drive.
7.) It will take a few minutes to analyze your files, but eventually a list of things to delete will appear with little check boxes next to item. Go ahead and check every thing except for the last one that asks if you want to compress the files on your hard drive.
If you're running XP, then you could also defragment your hard drive before you sleep.
1.) Start
2.) Programs
3.) Accessories
4.) System Tools
5.) Disk Defragmenter
6.) Defragment your C:/ drive.
7.) Let your computer do its thing for a few hours or until it is done defragmenting.