Basic Hardware Primer
No matter what platform you intend to use (Windows or Linux - MediaCenter, Media-Portal, MythTV, FreeVo or any other) there is some basic hardware that is required by all.
The OS and what types of media you want to record or play will have an impact on the type and speed of the processor.
For instance, if all you want to be able to record is standard analog cable TV with standard stereo sound on a Linux based MythTV system, you could probably make do with an older PC you have laying around. A Pentium 2 600Mhz with 512MB RAM would probably work well enough.
However, If you want to record HDTV with full Dolby Digital surround sound. You are going to need something a little more powerful. Like a Pentium 4 2.6Ghz HT or more with 1GB RAM.
Video Card -
You're going to need a fairly high-end video card. This is probably the most important piece of the system. If you get a low quality card, you're going to get low quality video, it's that simple.
High quality doesn't have to mean expensive. I'm using an MSI nVidia 660GT based video card, it supports DirectX9(required for MediaCenter) has a built in MPEG decoder and 128MB RAM, it has DVI, VGA and Svideo output. So I can attach it to whatever type of display I want to. The card cost $129 with a rebate.
SDTV and Cable-
The most common cards in use are the Hauppauge PVR- Series. They come with a variety of features depending on what you want. I'll explain the basic differences here. If you want more in-depth info go to the PVR webpage http://www.hauppauge.com/pages/prods_pvrs.html.
WinTV-PVR-150: PCI bus card with 125 channel cable-ready TV tuner, hardware MPEG-2 encoder, dbx-TV stereo, S-Video/composite plus audio inputs. Includes an IR Blaster to control a Set-Top-Box.
WinTV-PVR-250: PCI bus card with 125 channel cable-ready TV tuner, hardware MPEG-2 encoder, dbx-TV stereo, S-Video/composite plus audio inputs. Same video quality as the PVR-150 without the blaster.
WinTV-PVR-350: PCI bus card with 125 channel cable-ready TV tuner, hardware MPEG-2 encoder, hardware MPEG-2 decoder, dbx-TV stereo, FM radio receiver. The difference here is the MPEG Decoder, in most cases, it's not worth the hassle of installing this card since if you are planning on HDTV you cannot use the decoder.
WinTV-PVR-500: PCI bus card with Dual 125 channel cable ready TV tuners, each with a dbx-TV stereo decoder, Dual high quality MPEG2 video and audio encoders based on the Conexant -416 MPEG encoder, One back panel composite/s-video plus stereo audio inputs to connect to cable or satellite set top boxes, Two on-board A/V headers, to connect to two more A/V sources (A/V cable set not included), One FM radio receiver.
Most of the other video capture cards are either clones of the hauppauge or do not have a built in hardware encoder. The hardware encoder is not *required* but if you use a software encoder you are putting a lot more stress on the CPU and you may get stuttering and lots of video defects if the CPU can't keep up with the video. There are too many vendors and cards available to try to list here.
HDTV Tuners -
ATI HDTV-wonder. Discontinued, but still available from some vendors.
AVerMedia MTVHDA18 A180
KWORLD ATSC-110 PCI Interface PCI Digital / Analog HDTV Tuner
ADS Instant HDTV Tuner PCI Card
DViCO Fusion Tuners. There are about 10 different models of HDTV cards from DViCO with different features and prices. Including a Dual-Tuner HDTV card! These cards are tough to find but are well worth the price.
Sound Card -
Again, depends on what you want to do. If you want basic stereo or ProLogic surround sound, you can use a regular built in or add in sound card and use the line-out to some type of receiver or amplifier. If you want full Dolby Digital or DTS surround, you will either need a sound card capable of decoding those audio signals or has a digital out to an A/V receiver that can decode them.
In order to receive Over-The-Air (OTA) broadcasts you need some type of antenna.
Where you live and what channels you want to receive determines the type of antenna. If you live fairly close to the broadcast antenna and only want to get those channels, you might be able to get away with a small tabletop antenna. The further you live from the broadcast and the more channels you want, the larger the antenna.
The best way to see what you would need for an antenna is the Antenna Web site. Type in your address, type of house (how many floors) and whether there are trees in the way. AntennaWeb will give you a list of all the channels you should be able to receive and the type of antenna you need to receive them. This doesn't guarantee that you will receive those channels as there are other factors like hills, valleys, forests and building that could be in the way, but it's a good place to start.
That's it for this primer, I hope it helped.