If you have aging Windows XP and Windows Server 2003 machines that have filled up their C: drives, here’s a Microsoft KB with documented safe files you can remove:
KB 956324 – How to reclaim disk space on Windows XP and Windows Server 2003-based computers.
To cut to the chase on which Windows Update files you can delete (there are other directions in the KB as well, but these are what most server admins will be looking for) are below (taken from the KB as of 9/4/2012):
Warning If you delete the folder for each update, the corresponding Windows update cannot be uninstalled. Consider the effect that this will have on the computer before you delete the Windows update files.
To delete Windows update files, follow these steps:
Warning If you delete the backup folders for each Windows XP service pack, you will be unable to uninstall Windows XP service packs.
If you delete the folder for the installation files and the cache for the Windows XP service pack, you will be unable to restore corrupted Windows XP service pack files or to install additional Windows XP features that are not installed by default. You may want to keep a copy of these files in another location. For more information about how to keep a copy of these files, click the following article number to view the article in the Microsoft Knowledge Base:
Consider the effect that this will have on your computer before you delete these files.
To delete Windows XP service pack files, follow these steps: