You cannot put them on a shelf like a normal tool. It's a mel script I found mine by just putting "maya x-ray script" into google. I think there is also a script in highend3d. Just have a look it only takes five minutes to get it.

Just out of curiosity what kind of mac do you have, cause I'm thinking of getting a new one (I really don't want to go back to windows) At the moment im running maya on an Ibook g4 900mhz.....:angery: and as you can imagine it sucks!