Hmmmmmm..... just think... find a spray on water proof coating, spray all the boards in the computer, waterproofing everything. Then, mod the case to have a nice window in it, fill with water, insert fish. Heat from components will act as the heating element for the new aquarium. You'll need the caulk to seal the case.
Wow, I typed that as a joke, but... that sounds almost worth attempting to do!
I could use one of those clear epoxy resins to coat everything..... remove the fans, but keep the heat sinks... it just might work! Of course, then it'd be a pretty permanent setup...