Absolutely, what he said
For the VIP 622, the 2nd output (to tv 2) is always SD, even if the source is an HD program. So I watch a small amount of HD content on the SD output, and I have to say it still looks good. Obviously not HD, but it does look better than the regualr SD channels, by far.
So if you had a 622, and you had it outputting to two SD TV's, and you subscribed to the HD package, then you would basically be getting a number of new channels with the best SD picture you are going to be able to get!
Of course I would recommend then getting an HDTV at some point, it is wonderful.