When windows performs it’s updates, often but not always some of the hot fixes leave backup files so that you can later uninstall those hot fixes should they themselves be a problem. Normally these backup files present no issue and can simply be ignored. On the occasions where this is not the case and you need or simply want that space back, there is a free tool to help.
The tool is call xp_remove_hotfix_backup.exe and can be downloaded here http://www.dougknox.com/xp/utils/xp_hotfix_backup.htm .
Its a good idea to exercise some caution before using this tool as when it’s done cleaning up the backups there is no going back. You can still uninstall hot fixes applied to your system, but those same hot fixes will no longer be able to restore the files they changed before they were applied. This tool is quite speedy and frees up a suprising amount of space, but unless you’re going to be worse off for waiting, I would not run the tool directly after applying new updates.