If you have an older DCT-6412 with HDMI (large white rectangular with a bunch of holes, and one slot), then you can use that for the video. You just need an adapter, or a cable with HDMI at one end and DVI at the other (I use one from Amazon, as it's cheaper than an adapter!) The only drawback is that DVI doesn't carry audio, so you would need to either use the analog audio ouptuts to your TV (most TV's have one HDMI input that also has an analog audio input), or send the audio (analog or digital via coax or optical) to a separate receiver.
John please remove your email address, this is a public forum and you will get spammed.
You are welcome to take the DVR and remote to the local Comcast office for a exchange for a HDMI DVR. As equipment varies day by day as equipment comes from the warehouse, there might be days that they don't have a HDMI DVR that specific moment, the guy in front of you might get the last one. There's a lot of recycled equipment out there.
In the mean time, you should hook it up to one of your component cable inputs on your TV with a component cable with a red/blu/green video and red/white audio cable. This will still give you full HD at 1080I and 720P that comes from teh broadcasters.