I've heard of people cooling water rigs with small (dorm-sized) refrigerators. It's easy enough to build in its simplest form, just put the rad in a fridge (maybe submerged in a liquid) and use some extra tubing and a drill to close the loop back to the case. A pelt on the reservior or radiator doesn't sound like such a good idea to me. You would need to cool the hot side of the pelt somehow, and the efficiency would be very low.
If you want to use water-cooling and a pelt, you're better off putting the pelt directly on the CPU, and water-cooling to remove heat from the hot side of the peltier. Do a google search and I'm sure you'll find a bunch of pages with such projects in some form or another.