C:\Windows\$NtUninstall...... folders (hidden) - Especially $NTUinstallServicePack $MSI3Uninstall (MS Windows installer 3?)
BUT NOT windows\servicepackfiles as they are for future wincomponents add/remove
C:\I386\ C:\Windows\Driver Cache\I386\ C:\Windows\ServicePackFiles\I386\
I386 folder contains setup files (including hardware drivers)
C:\Windows\Downloaded Installations\ C:\Windows\SoftwareDistribution\Download\
C: WINDOWS Temp
Docs&Settings-> Local -> Temp Internet, Temp
Be aware of hibernation, turn off sys restore too! C:\HIBERFIL.SYS
tool Unlocker (download: http://ccollomb.free.fr/unlocker