The coating everyone is referring to is the Anodized aluminum... on a hardness scale, it's about as hard as diamond, but is formed by a chemical process, so it can be stripped pretty easily.
Soaking the metal in oven cleaner is the easiest homemade method for this. After the anodizing is removed it will look really bad, but THEN, it can be buffed to a shine, or get it re-anodized or chromed...
I was contemplating getting my 12" re-anodized in red before I sold it (have a macbook 13 now...- call up a few local rim shops, most do in-house anodizing, but will need the parts stripped of all plastic first.
on the 12 and 15" powerbooks the lcd cover comes off after removing the screws at the base of lcd face, then working around the edge with a plastic stick. pop off the cover, then remove the AP antennas to get it the rest of the way off.
Powder coating would work- that's paint, but please don;t try to buff the surface unless you have enough service parts on hand to fix the mistake