Building an HTPC on the cheap
PVRWire has taken the time to give you a quick write up of how to build a cheap HTPC. Also contained in their article is a link to another such article. If cheap isn't your thing, Matt has a similar write up on preparing yourself for a HD HTPC.
From the article:
Processor: AMD Athlon 64 3000+ because it's reasonably fast, and since it's a Socket AM2 chip, there's potential for upgrading.
Motherboard: The MSI K9GM2 has an onboard graphic accelerator, with support for TV-Out and NVIDIA's Pure Video Decoder. By getting a motherboard with onboard graphics and audio, you can save the money you would have spent on three separate devices.