1. Install WinDirStat (never really investigated to see if it is malware free. oh well) – to see where space is going away.
2. Run the usual disk cleanup.
3. http://everythingsysadmin.wordpress.com/2011/03/16/cleanup-winsxs-after-windows-7-sp1-install/ cleanup c:\windows\winxsx ( winsxs folder ) as it was too big. Used this command (run as admin):
DISM /online /Cleanup-Image /SpSuperseded
The folder went down from 13.5GB to 8GB (Still a lot – i know). I think this is after SP1.
4. delete %temp% and any other temp directories.
5. run CCleaner to clean old crap (http://www.piriform.com/ccleaner) – too bad it tried to install a toolbar during install.