Rey_1178, overall it sounds like you have more horse power in than my laptop does and it does great most of the time so you should be fine as well.
Big Dawg 23, I have the Hauppage 950 and I see some of the same things for processor usage on my computer while watching live TV. The issue is that the USB tuners have software encoders so the processor has to do all that work. If you have an internal card that did hardware encoding it probably wouldn't be an issue. I haven't looked at my processor usage while watching a pre recorded HD show on my laptop, but I'll look at that tonight.
If you're using OTA analog then you will definitely see a hit for software encoding. OTA HD is already encoded, so if you're watching OTA HD live or recorded, your system is mostly decoding.
OTA HD is MPEG2 based, which is less cpu intensive than D* HD which uses MPEG4. Software decoding of MPEG2 or MPEG4 is a cpu issue, just about any old video card will work if you have enough cpu. If you don't have enough cpu, modern video cards can offload some decoding. Ideally you would have something like an NVidia PureVideo based card (or ATI equivalent) which accelerates playback. This offloads decoding significantly and will let you get away with a slower cpu than pure software playback. I'm assuming your box will also need to decrypt the video stream as it is decoding it for playback.
I'm guessing more requirements details will surface, but one measure might be that if your system can playback Apple's HD 1080 movie trailers with cpu to spare, it will probably be pretty decent for decrypting and decoding. If your system is struggling with Apple's HD 1080 then I would guess this would be too much for it.