Oh, and before I forget, get yourself some "aircraft paint stripper" at the local parts shop. It's about 6 bucks a can, and will eat ALL finishing product off of the wheel in a matter of about 5 minutes. (Best used on a wheel that doesn't have a tire mounted). Then just lightly scuff up the alloy rim itself, and commence to spraying evenly with VERY light coats. They'll dry fast but I still recommend you wait about 5~10 minutes between coats, for proper bonding.
One more thing, make sure you get a paint that will bond to metal alloy nicely. I used crate motor paint on mine, and it's almost as if I powdercoated them.