The case is NOT grounded, it is NOT electrically connected to the motherboard via the screws that attach the motherboard to the case. The case prevents the electromagnetic fields from causing interference, but it does not need a connection to the powersupply (or motherboard) for that. You can safely paint the case.
Clean the case with degreaser (white spirit or ammonia), dry well and then spray with automotive paint or any paint-in-a-spraycan. For a really nice job you should spray a primer first, very lightly sand it when dry and then spray the final color.
If you've never spraypainted before practice on a test piece first. Basically you don't want to start spraying while pointed at the object. Start spraying next to the object, then move over the object in a fluid motion, continue until you are no longer spraying on the object and then stop spraying. Spray slightly overlapping strokes.
It's better to apply several thin layers than one big droopy mess.
Work cleanly and neatly, pay attention to what you're doing and nothing will go wrong. It is easy, once you get the hang of it.
6The inside of your case? – Ignacio Vazquez-Abrams – 2010-04-23T01:22:17.550
yes, the inside. – Liam teague – 2010-04-23T02:09:59.083
2are you going to take the parts out, then spray?? a little confused here... – studiohack – 2010-04-23T02:11:11.547
3please remove your hardware first. – Raptor – 2010-04-23T04:19:38.827
why list your computer specs if you are trying to 'spray paint' your case? ;) – Jakub – 2011-02-23T16:10:51.467
4@ShivanRaptor: don't you want to know what happens if you paint it with the hardware in? – Jonathan. – 2011-02-23T16:11:35.067
@Jakub: I would like to see the results :P – Raptor – 2011-02-26T15:20:42.760
Please remove your software first. (Otherwise, the spray paint will melt into and blend with your software.) – Mateen Ulhaq – 2011-05-24T03:35:01.343