Get a container of 'aircraft stripper' from the parts store (Advanced, Autozone, etc.) and brush it on the entire wheel letting it set until the paint bubbles up into an apple sauce like texture. While wearing gloves scrub the rest of the paint off with a "scotch pad".

Spray off the wheel removing the aircraft stripper paint sludge.

Sand any rough spots smooth using various grits of sand paper then clean and wipe down the entire wheel with paint thinner. (NOTE: If the tire is still on the wheel then make sure you clean the groove between the wheel and tire extremely well, preferably use an air gun to blow out any excess stripper or thinner or it will ruin the fresh paint.)

For a rattle-can spray job i'd suggest Duplicolor Wheel Paint. http://www.duplicolor.com/products/wheel.html

Making sure you're in a relatively warm dry space, spray light coats on it every 15 minutes or so until its covered. I'd strongly suggest spraying the grooves and tight spots first then the face of the wheel last.

Wait a few days then you can polish and wax it like you would the paint on a car.