http://www.boxgods.com/dept/modding/index.php?Action=Article&ID=198 I didn't read the guide but it looks good. Make sure to use the same brand primer as you do paint. And read the instructions on the back of the can, drying times can vary by manufacturer
http://case-mods.linear1.org/category/painting/ read his two part guide on how to paint a case. If you do what he says it should turn out looking real nice