Noobish questions

My 1st generation TiVo and my DVD player are both on the way out, so I want to replace them with a HTPC. Here is what I am looking to build for a HTPC


* Dual tuner, HDTV OTA

* Quiet / Fanless

* Upscale standard DVD to HD

* Play HD DVD (HD-DVD, BluRay, etc) at HD resolution


So here are my questions:


1.) What is the difference between Vista Home Premium and Vista Ultimate when it comes down to MCE / HTPC? AFAIK there is no difference, but I'm afraid I'll buy the OS and then figure out that that Home Premium only supports 1 tuner or something silly.


2.) What is the difference between NVIDA 7050 and NVIDIA 7050PV chipset?


3.) The mean-n-potatoes of the system that I'm looking to build includes a motherboard with NVIDIA 7050PV chipset, Athlon 64 LE 1620 2.4GHz, and a Hauppage 1800. I'm going to use the onboard Video of the 7050PV, which is supposed to have HDCP. I'm hoping the Athlon is cool enough to run without a fan, especially if I underclock it.


With that in mind, does this have enough horsepower for my requirements?