Chris Lanier has some very helpful links for working with Windows Media Center (both XP and Vista)’s DVR-MS recorded TV files. In his first post, he links to DVRMSToolbox, a free set of tools that let you convert DVR-MS to MPEG-2, MPEG-2 without commercials, WMV, WMV without commercials, WMA (audio), as well as edit DVR-MS and save it back in its native file format. I’ve heard the automatic commercial detection is pretty good.
His other post contains a registry hack that will let Windows Movie Maker open DVR-MS files. Once you’ve done the hack, you can use Movie Maker (including the excellent and powerful Vista Movie Maker) to edit, mashup and export the recorded video in as many ways as you want. You could even import an entire season of a TV show, edit out all the boring parts, and have your own clip show!