Hi darkload, I am not aware of freeware applications that can directly edit DVR-MS files. Alternatively you can convert these files to unencrypted MPEG2 or WMV9 files and then edit them.
DVR-MS to WMV9 with WMA9 Professional 5.1 Channel
The guide converts the DVR-MS stream to XviD/DivX. You can then your VirtualDubMod or anyother application to edit them.
Cheers,
McoreD