It really depends on the outputs from your DVR as your computer is probably more flexible than it. My DVR has S-Video and Component (RCA) type outputs but no digital output so I have to go though the "analog hole". That means going from digital down to analog and then doing a capture back to digital. I use a Canopus firewire interface for my computer but it sounds like you've got a capture card like an "all-in-wonder" card. Don't forget that S-video is better quality than Composite and that it has no sound so you'll have to run a second set of cables for the audio.

I haven't seen a DVR which will allow you to do digital dubs yet.