I did my Psion 3mx in "Monaco Blue" metallic... It looks quite good - much better than the peeling rubber paint that Psion used.
I used:
Halfords plastic primer spraypaint
Halfords Monaco blue spraypaint
Halfords clear lacquer spraypaint
500, 800, 1200, 2400 wet and dry paper.
It's *all* in the preparation. Spraying is actually the quick bit.
Oh, and a lot of it is in the waiting for the paint to fully harden, too. Don't be tempted to do things before it's all properly cured!
It starts out as a fun job, but then it gets slightly tedious IMHO, but the results are worth it