Tr clicking on "start">"programs">"accessories" then "tools" (or maybe "system tools"). About the second or third down should be "disk cleanup". Click it. There'll be whirring and grinding from the hard drive, and an application window will eventually open up with a range of options for file deletion, including temporary files, temporary internet files, recycle bin, maybe a few more.
Tick the checkboxes beside each one you're happy to have cleaned. (When you click on each one, a small block of general info will appear in the lower window regarding what's going to be deleted. Make your selections, click ok, wander away for 20min or so...it might take a bit less, or a fair bit more, if there are a lot of files.
Be interesting to see how many Mb can be gained from this, and if scandisk and defrag will work ok afterward.
How long has it been since you did a virus and antispyware scan? And how long did it take? And was anything found?
Mark.