Defragment your hard drive
The space on your hard drive is divided up into a large number of small equally sized locations. Files take up a number of these locations depending on there size. Over time, as files are moved around, gaps of space will appear. When the computer tries to write something to the disk, it might find the space is too small to fit the whole thing, so it has to put the rest of the file elsewhere. This is called fragmentation.
As the computer tries to access the file, it has to jump about all over the place picking up all the pieces.
This slows down your computer.
A de-fragmentation program will rearange the data on your hard drive to put the files back together.
You'll find the windows defragmenter here: start > programs > accessories > system tools > disk defragmenter. On average it should be done about once a month.

