Umm... I think credit should go where it's due. This was first posted by Snazzy in 2006 on the Planted Tank forums:
http://www.plantedtank.net/forums/diy/36257-diy-external-heater-56k.html
Incidentally, at the start of his post he writes: "Please do not post this anywhere else without my permission!" Jcardona - did you ask before posting his tutorial here?
We4weiners - the Hydor ETH heaters are generally very well reviewed. I've had good experiences with the 300 and 200. The 201 appears to be a new model and I'm not sure what distinguishes it from the 200.