In WinServer2K8, the WSUS (Windows Server Update Services) information can (with time) take up quite a bit of space. The Server Cleanup Wizard (found in the Windows Server Update Services console - C:\Program Files\Update Servicesqadministrationsnapin) can remove unused update files, old revisions of updates, etc. It can take a while, if not run for a long time, first select everything but the first option (Unused updates and update revisions), after that's finished run it again with this option.
This (and other ways of regaining disk space in Win2K8) at the Technet blog.
Edit: also select and decline superseded updates.
