Like what Operandi have said. Go with AMD. They can do the same thing and have better graphics compared to Intel. To include what Operandi have said, AMD is cheaper overall. Intel might the fastest at this time, but AMD is better for HTPC. Also do not look at TDP because this is a false way of power consumption.
The bare minimum for the processor depends what you are going to do. Flash consumes a lot of resources, so I suggest a fast processor such as an AMD Athlon II 250.
If you want to playback HD videos with ease, Linux is a lot better. The reason for this is Linux has less requirements to process HD videos. It requires a video card that supports VA-API or VDPAU, then you are ready to handle HD videos. The processor resources that are used is less than 20%. In Windows, you will need to have codecs that support HD decoding and you will need to use software that is compatible to run with your video card. Windows has a lot of layers for HD to work with fewest processor resources.
CableCARD type of tuners for computers depends on the compatibility with your cable service provider. I suggest talk to your cable service provider to get information what hardware are compatible with their CableCARD or else you will have a lot of problems. It is probably best to use a cable box for tuning to the desire channel instead of using an internal card. Some cable box models includes a IEEE-1394 or USB, so you can capture through that. Stand alone units works the best these days.
A lot of people think they should add a TV like remote to control a HTPC. This does not work for HTPC. I suggest the following to make it easier to control.
Adesso Wireless SlimTouch Ergo Touchpad Keyboard (WKB-4100UB)
http://www.adesso.com/en/home/keyboards/84-wkb-4100ub.html
Logitech diNovo Mini
http://www.logitech.com/en-us/keyboards/keyboard/devices/3848
I prefer devices that uses standard size batteries to make the device last long as it should.
If you insist on selecting Intel processors, you do not need to find a motherboard that contains an H55. This chip set has the ability to flip-flop between discreet graphics and on-board. For a HTPC, this feature is useless. Also it is useless in notebooks if you select a model that does not have two video cards. You are wasting your money when using a motherboard that uses H55 and using only one video card. The best video card is nVidia because of their software support in any operating system is the best. I have used ATI over the years and their software is pathetic. I strongly recommend to use Linux if you are going to use ATI graphic cards because the Xorg or third-party drivers works a lot better than what ATI can write.
I've got to disagree on this point.
If you're talking about just a generic computer then sure, an AMD one would be fine. But for an HTPC, you need HDMI output plus, preferrably, bitstreaming audio to get the most out of Blu-rays and other HD media. To my knowledge there aren't any AMD motherboard solutions that support those requirements.
You sound like an Intel fan boy that has been left in the cave too long. Since 780G, it supports HDMI output and as well as digital audio over HDMI. Bit streaming is none sense if you understand that anything happens in digital land will not affect the sound quality. If you are using inferior software, yes you will have problems with audio. Decoding audio into LPCM can be done with out any problems like what you are saying. At this time using a PC to playback movies is sad because it does not have the same features that stand alone units includes. For TV show watching, a HTPC is OK, but not the best. A HTPC is good at displaying web content, but it has limits of its capability. Though not all AV receivers or surround sound processors does not have enough power to decode an 8 channel audio from a movie and be able to process audio using custom environment settings like Audyssey, so LPCM might have to be used.
The original poster did not say they he or she will be playing back Blu-Ray movies. The original poster said that they will be using their HTPC for web content and TV show recording.