has created an interesting looking 3.5" PS3 Hard Disk holder for a school project. The inspiration for the the project was that 3.5" Hard Drives were a lot cheaper than 2.5" equivalents.
To quote: The case itself was constructed from black acrylic sheets (3mm thick for the dimension lovers out there) that were cut to shape with a laser cutter and moulded were necessary (i.e the top and bottom panels).
The pieces were stuck together using a chemical known as diachloromethane (I could give you the atomic structure if you wanted) which dissolves plastics before evaporating to leave whatever it was that was unlucky enough to be touching the plastic at the time well and truly stuck.
I used silver spray paint (I believe it was Ford Moondust to be precise) to spray on the motif and black fabric on the underside to prevent scratching. The HDD is held in place by a 2-piece bracket that sits snuggly within the curved panels of the unit to hold it tightly in place (or at least it would if I had the **bleep** screws).
One cable runs from the data socket on the hard disk to the PS3 and the other provides power from the mains with the help of an adapter.