i painted a frame with rustoleum last summer. If i were you i wouldnt spend the time taking the paint of the frame. id just sand it ti roughen it up a bit, spay a good even coat of primer on, then spray a couple good coats of paint on.
...but like jayrooney said above, this is not gonna look like a pro paint job or really anything close. I even put 5 coats of clear coat on top and mine still wasnt that great.

oh yeah, lightly sand between coats of color