DVRs store shows in an encrypted format, therefor just copying them to another device will likely mean you have tons of data you can't use.
As Dadiggle describes, if you can capture the playing of the files (73 hours is a long time and a lot of data) than you can get around the DRM restrictions, but at a loss in quality.
There are many links/forum entries that all say pretty much what Dadiggle said. If it were me, I would try to remove the HDD from the DVR and connect it to my Linux box to see what I might be able to pull from the system. But to be honest with you, I think you are out of luck on this one unless you do the ol' analog capture.
As a thought, you might give Easy VHS to DVD a try (http://www.roxio.com/enu/products/easy-vhs-to-dvd/standard/overview.html). Connect your DVR to the dongle provided and capture the shows as they play. It is a real time transfer and as long as you can connect to a device it will capture the audio/video.
It is an inexpensive way to try this as well.
Good luck!