Hi. There's an excellent tutorial on etching pedals here - http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album24/
A few extra tips -
Use standard cheap photo paper (from Staples/Costco etc). Try a couple of different types, thinner ones are probably better. PressNPeel blue is no better and much more expensive.
Iron your design on at the iron's hottest setting for at least 10 minutes and allow the enclosure to cool before you peel the paper off.
For your Ferric Chloride solution use a stronger solution than is recommended. Perhaps 1.5 times as much of the granules for the amount of water that it recommends. Also, try adding a couple of tablespoons of lemon juice to it.
Keep the solution warm! Room temperature is fine for etching aluminium, but the warmer it is the faster it will etch. i.e. don't keep it in your cold shed/garage/man-cave.
The Ferric Chloride solution is not too nasty at this concentration. It'll stain your clothes brown but it's pretty harmless if you get it on your skin. Stings a bit in cuts and I wouldn't think it's does you much good to get it in your eyes, so wear goggles. Also, if you were to dip a whole YY enclosure into the solution you'll get a LOT of flammable bubbles and a lot of heat. And a lot of mess. Don't bother trying it!
I hope that helps you get started.
Cheers,
Tim