Dudes, if Disk Cleanup takes more than a few minutes, it's because you have lots and lots of junk in your Temporary Internet Files folder. You can either go to Internet Explorer options and say Delete Files, or you can manually go through Windows Explorer to the Temp Internet Files folder (which is hidden in Documents and Settings) and delete the rubbish from there....

Disk Cleanup is good every couple of weeks... Gets rid of unwanted cookies and shit.

Even better is Disk Defragmenter. I advise everyone to use this atleast once in 10 days... Really makes your computer run faster.