if the two panels are in good condition, as in not needing bondo then i would advise that you just scuff it with red scotch bright pads
this should be sufficient for the new paint to stick to...
you just wanna scuff the shine off the panels...
to get better results use primer
and for even better results sand the primer with 320 before spraying
autobodydepot.net has all sorts of supplies as well as mixing your car's color and putting it in an aerosol can for you...
edit: and for a whole car, you can either scuff, or if you have a GOOD QUALITY palm DA you can run 120 then prime it, then 320 the primer, then prime again, then 320 again, then drop it off at the paint booth