If anyone (like me!) on a serious budget wants to save some cash, a box file has made a pretty reasonable case for my Mini ITX HiFi PC. It cost £2.58 from Tesco and holes are really easy to cut (being made mostly of cardboard). The ends are made from wood which gives it some additional strength. I'm using an external DC brick power supply, I don't think there would be room for a full size PSU. Inside I have a VIA fanless mobo, 2.5" samsung spinpoint HD and a Terratec soundcard. It hardly makes a sound. I have it mounted on its side with ventilation holes in the (wooden) top end. The power and hd led's are inside the opening catch and actaully look great. I've put 2 fans inside the 'lid' but haven't needed to switch them on at all. Oh yeah, quite alot of elephant tape is required to keep cables from shifting around too much.
(I freely admit to getting the idea from someone on ebay selling a pc in a box file)