to make it somewhat efficient, you'd need some sort of heatsink on the inside of the res to better transfer heat (just as a heat sink transfers heat away from the pelt).
there are units that run on a/c you can get made for fish tanks, already assembled for around $100. those claim they work fairly well, wether they do or not in a pc setup, who knows.
but, from what i've heard (you might want to check out the water cooling part of the forum
), this method isn't particularly efficient. much better to run on the cpu itself, although there are the obvious drawbacks of such.
but hey, try it out. pelts aren't too expensive, if you've got the power to drive them.