Video can easily be recorded into iMovie on a Mac using the analog audio/video outputs on most DVRs (using either a composite video or S-video output, along with right and left audio outputs). You do need additional hardware such as one of the ADVC converters from Canopus. This converts the analog video into digital video. iMovie sees the converter as a digital camcorder. You can edit the video (remove commercials, etc.) and burn to a DVD using iDVD.
With much trouble, recorded HD video can be transferred to the Mac via Firewire. One method is described in an article on the Macteens site (search the archives for "How To: Make your own Home Theatre Mac (HTMac)". The recorded video takes huge amounts of disc space.