Here's another question, is there a way to export a recording from the Comcast DVR to an extrenal hard-drive? The exported file would have to be in a readable format so that it could be viewed on a computer.
"is there a way to export a recording from the Comcast DVR to an extrenal hard-drive?"
Nope, there is no way. But even if you might be able to export a DVR recording to another device, it wouldn't be readable because recordings are "married" (encrypted) to the recording device.
To get a DVR recording to a computer you would have to play the DVR recording and capture the live playing stream to another device (DVD recorder) and then be able take the captured recording to a computer.
You can set up/build a HTPC (Home Theater Computer) with Windows 7, a TV tuner, and Comcast supplied/rented CableCARD. With a HTPC you have the possibility of unlimited recording storage/capacity, if you have the hard drive hardware to support doing so.