yea I want such a thing too for the same thing. I have DirecTV and TIVO and want to get it onto my laptop for flights. As far as I have seen so far it looks like the ATI USB 2.0 TV wonder is the best option at this point. Today the problem is that there is little to nothing that does not do the TV tuning and just does encoding from RCA jacks.
I'd get a ATI thing but they are more money than I am willing to spend.