I currently have two analog Hauppauge PVR-150s (on one PCI card) in my system
for analog cable, but I want to purchase a HVR-1600 to control my HD QAM
cable box (Cox Cable) to watch/record HD content.

Is this possible in Windows Vista Media Center? I have found some sources
that say Windows Vista Media Center will only recognize two tuners total.

If Media Center only recognizes two tuners, is there a registry hack or
patch to make it recognize three?

-Gina

So what you're saying is that I can install the digital tuner HVR-1600 and
Media Center will recognize it, but I will not be able to watch/record QAM
signals on it?

Is there any way that Windows Media Center can record in high definition
from a cable box?

It would be a lot easier to get a DVR from your cable provider.
As I understand it there are unscrambled and scrambled QAM signals. Only the
OTA channels in your area are usually unscrambled and maybe a few non HD
basic cable channels.
If you can receive OTA HD signals why bother with the rest, unless you can
get a CableCard unit, which is not likely.