Redditor Sirleechalot built this lovely Bioshock PC by submerging a media center PC in mineral oil (computers run fine submerged in this non-conducting fluid, though maintenance can be a little drippy/oily). The initial impetus was to build a system that ran quietly enough to be in his bedroom, but it took on a life of its own:

The motherboard and power supply are mounted to an acrylic sheet that sits in the back of the case. The tank is a 5 gallon Marineland tank. I ended up purchasing the mineral oil from ozbo.com. It's primarily used as a horse laxative. I placed a bunch of calls to local vets, but most of them wanted $18+ per gallon (and also thought i had some nefarious plans for their oil). The Big Daddy (ok, i guess Mr.Bubbles is more appropriate) figure was purchased from Amazon. I went to my local pet store for the tank, bubbler, pump, and gravel. For a power switch, i found an old cable from a computer i had built previously that had a jumper connector on it (the kind that would usually plug in from a case power switch) and soldered the other end to a momentary switch (these can be found at radio shack).