I've done it, my saturn is Purple with a Sailor Saturn logo on the top (I'll get a pic if I can ever be bothered to get my digi cam working). Basically, I find the best paint, is Acrylic car spray paint (I've been looking for shocking pink for my PS2), just make sure you remove everything from the case, spray at an evenly distance and make sure you put on three evenly coats(with pink, you may want to spray some white on before hand, some your pink doesn't come out dark), remember, very light coats, wait for the first to become tacky, then spray another coat. Once your happy with the colour, spray some laquer on the tacky paint as it still dries (harispray works wonders). Then your all done, my Saturn has been painted for over 2 years and it still hasn't faded or chipped.
Now I'm in the making of redesigning the case to look like the prototype PS2 case, If I'm successful, I'll post the instructions and designs. CYa