case modification

wouldn't work. A refridgerator works because it's an enclosed environment. If it's in the open it'll effectively cool nothing (the effect will be negligable).
If you do want effective cooling, use liquid nitrogen (helium is better but too expensive for most uses) cooling.

what do you mean its enviroment? the stuff in the refrigerator, or it being air tight? A case is not "in the open"

Your case has openings for ventilation...thus it is open.

who forgot to add the chlorine to the gene pool?

gee, covering the ventilation holes might help. Dont be an ass, an unoriginal ass at that.

We all get great ideas that upon further review reveal themselves as not being practicle, welcome to the club. Your average refrigerater cost around ten dollars a month to operate, so in the long run investing in a more convetional cooling system such as a liquid cooling system would be justifiable, that is if you're serious.

I have admit, for a moment I had a vision of this compressor and all of its support equipment piled up and attached to cardboard ducting with gobs of duct tape holding eveything to the side of the computer case with all of its vents taped over...a vision Rube Goldberg would have been proud of!

A full size refrigerator would be much to impractical yes. A mini-fridge is about the size of a case, and is more cost efficient. There is nothing wrong with duct taping the ventilation of the case. As far as the vents for the fridge goes, screws would work.

I know there are more practical ways of cooling your cpu, water cooling etc. But to do it just for the sake of doing it, thats why I want to do it.

Hey...go for it, and best of luck! About condensation, yep...depending on the amount of humidity in your local, that one could be a problem, but there are ways to get around that also. A smaller refrigerator doesn't mean that it will be cheaper to run, smaller compressors actually can draw more. Post a picture of this when you get it going, and let us know how it works.