I have been reading for quite a while, but I am afraid most of you guys are far more advanced than I am. Here is what I want to do, and I hope someone has already done this and can give me some pointers.
I want to build a mini-ATX computer for integration into my media center. I have been reading the post and I am looking at the HD HomeRun because it looks like it has all the items I am looking for, that being two tuners and QAM decoding.
The HD Homerun must plug into the computer by a network jack because that's all the output connections I see.

Does this have a Tuner or must I get a tuner card for the computer (I think the dual tuners are built into the HDHome).

Will Sage TV work with the HD HomeRun or should I buy MCE Vista.

I will need a Display card that has HD HDMI output...what works best

I think a SATA 300G hard drive is enough, do I need more?

I hope when I get it all together, I hope I can plug my Comcast cable into the HDHomeRun , connect it to my computer by the network cable, and tune in the local network stations in HD and record them on the hard disk. Will this will work and anyone has done this I would very much appreciate their advice

There's a huge HD Homerun thread in the HTPC section that should answer all your questions.