When a service pack or a hotfix is installed in Windows 2000 and XP, the user has the option of backing up the replaced files in the event something goes awry. This is always a good idea, because the effects of a given hotfix or service pack (usually hotfixes) are hard to predict in advance.
However, once you've tested a given fix and found it to be working perfectly, you can either move or delete the backup files. Over time, the accumulation of backup files can put a dent in the free space the system directory uses. If you want to free up this space, you can delete these files or back them up and move them offline, rather than deleting them completely. If the hotfix does need to be removed in the future, you can put the backup back into place and undo the hotfix.
The files for a given service pack or hotfix are in hidden folders in the %SystemRoot% directory. The folders in question are named with the convention $NtServicePackUninstall$ (for the most recent Service Pack) or $NtUninstallKBXXXXXX$, where XXXXXX is the number of the Knowledge Base article that describes the hotfix. For instance, the backups for files replaced by the hotfix addressed in Knowledge Base article 828026 are found in the directory $NtUninstallKB828026$M. Sometimes the format is $NtUninstallQXXXXXX$, you can see both formats in the same machine. You can simply copy out or delete the folders, but you'll have to keep the naming convention and the contents intact.
To delete the Registry key that holds the uninstall information for a Service Pack, look in HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionUninstall for keys with the format KBXXXXXX or QXXXXXX. Once again, you can export the keys in save them separately, and then restore them in the event that you have to remove a given fix elegantly.
Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter. Check out his Windows 2000 blog for his latest advice and musings on the world of Windows network administrators – please share your thoughts as well!