I had occasion to open the C:Windows folder on my old XP machine, and was immediately struck by the number of folders whose names began "$NtUninstall". They were from several hundred kilobytes to 10 megabytes in size, and there were more than 150 of these bad boys just taking up space on my hard drive. There were also a few multi-megabyte files whose names began with "$MSI31Uninstall" or "$NtServicePackUninstall". Some of these folders dated back to when I bought the machine in 2003.
If Explorer won't show you the contents of the C:Windows folder, click Tools > Folder Options > View, select Show hidden files and folders in the Advanced settings window, and click OK.
These uninstall folders are intended to roll back the system in the event of a Windows patch gone bad. Obviously, the OS updates they refer to had done no harm to the machine, which is working just fine. The PC's 30GB hard drive has 5GB of free space, which is slightly less than the 20 percent margin many experts recommend to ensure a smooth-running drive. Clearly getting rid of these unnecessary patch fixers would do my system good. To play it safe, I retained the few uninstall folders that were less than a month or two old.
Unfortunately, the files aren't listed by date, and if you click Date Modified in Explorer's Details view, the uninstall folders get mixed up with other folders in C:Windows. Rather than selecting the uninstall folders one by one, I clicked the first one I wanted to delete, then Shift-clicked the last one, and finally Ctrl-clicked the few recent ones I wanted to keep to deselect them.
The fixes will still be listed in XP's Add or Remove Programs Control Panel applet. To remove their entries, open the program, check Show updates at the top of the window, scroll to Windows XP - Software Updates, select each one at a time, and click Remove. You'll get an error message telling you the file has already been deleted. Click Yes and move on to the next one. Just be sure not to accidentally uninstall an update that you haven't already deleted. If the Software Update Removal Wizard opens rather than the "already deleted" error message, click Cancel.
Play it safe by keeping the folders in the Recycle Bin for a week or so. If you experience problems with a Windows patch for which you've deleted the uninstall folder, simply locate it in the Recycle Bin, right-click it, and choose Restore to return it to the C:Windows folder.
I found only two of these patch-uninstall folders in the C:Windows folder on my Vista PC, both of which were empty. I don't know if that means Microsoft figured out a way to safeguard its Vista fixes without cluttering up your hard drive, or if the update-uninstall folders are now stashed somewhere else.