When I were a lad (and it were all fields round here) I decided to respray my RG250 black (coz it would look c00l). No preparation, no airbrush, just a couple of coats of Halfords finest straight out of the can.
It looked like a turd.
63 is right - do it proper
EDIT: Oh, and do it outside or in a very well ventilated area, and wear a breathing mask. Skimp on that and your lungs will look like those of an eighty year old forty a day smoker.
EDIT 2: Just remembered, I did my RG250 outside, caught many many flys within the paint
Perhaps a shed, with windows open might be a better bet.