Try this:
How to Transfer Video From a Dish DVR to an External Hard Drive | Science - Opposing Views
Though I've never been able to pull off what you're trying to do with DISH. DirecTV, I think, is the service that makes you buy a program from them to download video you've DVR'ed. I tried what that link above suggests and never was able to do it. Might be a separate unit you need to buy for DISH also, not sure.
Interested in any other responses of successes.