The default setting of Internet Explorer saves a ton of temporary files to your hard drive - it is a real mess and a real waste of hard drive space. You can open up Internet Explorer and go to Tools - Internet Options. Delete the temporary files and offline files. This can free up a lot of space. You can change the setting so that the hard drive space allocated for this is lower. I often do 20 MB and it works fine.
You can always clean up your hard drive manually. Sort through your files and see what to keep and what to remove. The My Documents folder often has a lot of files you don't need.
windows XP disk cleanup problem 
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