Build Your Own Home Theatre PC Part 1
 

"The first step in the process of building this system would be to select a suitable HTPC enclosure. Case selection is rather subjective and just about everyone will give you an opinion on the type of enclosure to use.
Budget consumers can minimize costs by using anything from a standard desktop case, mid-tower or server case. For those individuals who consider themselves HTPC purists, there are HTPC style enclosures that have been designed to resemble the look and feel of stereo or home theatre equipment."

http://www.modthebox.com/htpc.shtml