I came across a nice trick to free up quite some space; In the folder C:\Windows\Installer are a lot of files not being used at all anymore.
To ensure the uninstallation of programmes is still running smoothly I searched for a small utility called MsiZap.exe which can be downloaded from the Microsoft site http://support.microsoft.com/default.as ... -us;290301
It cleans out all the orphaned .msp files and gave me the first run 4,5Gb of cleaned up space.
Some further instruction can be found here:
http://blogs.msdn.com/heaths/archive/20 ... tches.aspx