LOL. Don't spray in a dusty environment.
Use enamel paint for spraying plastic parts.
You should also sand your case before priming it. Let it dry for 24 hours. If necessary sand it down a little with a fine grid sanding paper.Clean again and then spray a few coats of black enamel paint.
For aluminum parts use a different primer. Or it won't stick.
I used Duplicolor paint and it's very good.
The mnpctech is a very good guide. For a good result do it like that.
But then again you have to know how to paint!
I was gonna say something about the dust... the only real answer is keep your workplace cleaner and work in a less dusty environment. A common theory is that painting should always be done outside so you don't inhale fumes - on the contrary, how many professional paintshops paint cars etc outside? Mine was painted in the garage with all the doors shut, then I exited the room after the job and let it dry. Opening the door would have just let dust and poop fly in and stick to the paint.
And always make sure you use the right paint for the job - primer for steel won't specifically work on aluminium or plastics, plastic paint won't work on metals, and so on. Technicks' suggestion of Duplicolor is a good one, they make some damn fine paints. I personally used PlastiKote with good effect.
The iBook is getting sprayed too shortly, but unfortunately because of Apple's selection of materials, I have to use expensive Tamiya sprays - the body is polycarbonate.
