Only the Fusion (3 Gold and higher) and MyHD (130 and higher) cards work with QAM (cable). All others at this point can only do OTA (antenna). The HD channels you can get through cable is a big YMMV. Basically you should be getting whatever isn't encrypted, which should be all the basic network channels (FOX, NBC, CBS, ABC, and PBS). If you're lucky, you might also get INHD1,2, Discovery HD, ESPN HD, HBO HD, Showtime HD, and whatever else is unencrypted in your area, although technically you should be subscribing to get these extra channels (they are normally encrypted). Check your local listings to see what's available in your area. To get encrypted channels, the only way to currently get them is to subscribe to HD service from your cable company and use their box or a CableCard.
The Fusion is cheaper and works with MCE, but the software that comes with it sucks. But the problem with MCE is that you need a compatible analog card (ie on their list) to install it (even though the Fusion has analog), and MCE (currently) only works with OTA, not HD cable (although this will supposedly be fixed in future releases).
I only have the Fusion3, and not the MyHD, but from what I've heard, the software on the MyHD is MUCH better--however, it doesn't work with MCE. Hope that helps!