Problem solved, (thanks to <http://www.heise.de/netze/news/foren/go.shtml?read=1&msg_id=12983409&forum_id=119217> - in German)
- Hold the option key and drag /System/Library/CoreServices/SystemVersion.plist to the Desktop (makes a copy)
- in this Desktop copy, change both "10.4.10" strings to "10.4.9" and save
- option-drag the Desktop copy back to /System/Library/CoreServices/ and replace the original
- install TSM
- in the Desktop copy change both "10.4.9" strings back to "10.4.10" and save
- drag the Desktop copy back to /System/Library/CoreServices/ and replace the current version
- Finished