In order to remove these restrictions, Microsoft released Windows XP Media Center Edition. This is designed for OEM manufacturers such as Sony, Dell, or Gateway to sell to the consumer in a media friendly boxes designed to sit in your living room, plug into your TV, and work as computers that you can use from the comfort of your couch. Well, if you look around at some online retailers, you can find Windows XP Media Center Edition 2005 available as an OEM version, meaning you have to buy some hardware to qualify for this purchase. No problem there, as we decided to buy quite a bit of hardware all at once to build a computer that would look and sound like a home theater component..You can check it out over here.
Quiet HTPC system building guide

Corsair learns us how to build a silent home theatre PC system.