I don't feel it's really worth the trouble/money to do this. I seriously considered it many times and never ended up going forth.
You can just upgrade the fans to the Whisper Max and bolt-mount the heatsinks. That should effectively eliminate the chance of it RROD'ing, and it'll run cooler. See here:
http://www.hardwarecanucks.com/forum...n-upgrade.html
If you seriously want to watercool it though, I'd suggest buying the Lian-Li case and using that. It has a 120mm fan in it already, so mounting a single 120mm rad would be effortless. Also tons of space inside (due to having a 120mm fan), so getting the pump and reservoir in there wouldn't be a problem.