Like what was said above, you can record anything that plays through your TV's speakers with the HD PVR because it is catpuring everything that is coming OUT of the device/system/TV. Your voice however is a little bit tricky. there is a way to do it, but it is quite difficult and I honestly don't know how to do it. Just buy a cheap Mic and have it record your voice on the computer. Audacity is free and will capture your voice no problem.
Once your Yeti comes in, you'll be fine! Just until then don't count on capturing your voice. Just do post commentary
Best of luck!