Microsoft Windows XP comes with a utility called Disk Cleanup. You can find it by going to:
Start Menu -> All Programs -> Accessories -> System Tools -> Disk Cleanup
If Disk Cleanup is taking an annoyingly long time to start up because it is ‘scanning for old files to compress’, you can force it to stop this scan. All you need to do is modify the registry. Using regedit.exe or similar tool, browse to this key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer\VolumeCaches
Find the ‘Compress old files‘ registry key and rename it. Save and close.
You can find Microsofts knowledge base article on this here:
http://support.microsoft.com/kb/812248