Hi E.,
When everything goes HD(I meant to say digital--I had HD on the brain:), then if you have a set top converter for cable, you should be fine. You would only need an HD converter box if you used an antenna to watch tv(I didn't even know you *could* watch tv w/out cable!).
Cable boxes are only for "premium" channels and anything above basic. HBO, Cinemax, Showtime, Starz, etc are premium, and if you want the music channels, or to watch movies/shows On Demand, then you'd have to have a box for those also. Alot of other channels are considerd above basic also, but I don't remember which ones.
Try going to Comcast's website(if you use them) and see if they have a basic channel line-up.
Believe me, I feel your pain. I was thinking I'd like to cut our cable bill waaaaaayyyyy down too, but we need our box for the DVR and I admit, the music channels are an indulgence of mine I don't think I would want to do w/out.
Good luck, and let us know what you find out.
K. W
P.S. here is a link to learn about the digital switch: http://www.dtv.gov/index.html