Here is a server that was specifically made to do protein folding simulations for the fold@home project. The enclosure is a 4u rackmount tray with nuts glued in to accommodate the motherboard's mounting screws. The power supply was clamped in place using crosspieces that came with the enclosure. The hard drive is attached using heavy duty velcro.
This server has 1GB ram, a single core athlon 64 x2 processor, a gts-450 graphics card, and a gt-430 graphics card.