A clean registry
A computer's registry accumulates a lot of corrupted, unused, and unnecessary registry keys, especially if keys are not removed when you uninstall a program. As a result, you may begin to experience problems and your machine might function slower than expected.
The latest version of Microsoft's RegClean could delete a lot of such registry junk. You can download this from ftp://ftp.microsoft.com/Softlib/MSLFILES/REGCLEAN.EXE.