It's really not all that hard to paint a tank, and it can be easier or harder depending on condition and your aims. If it's really rusty, I say use 60 grit sandpaper, get it down to bare steel, sand it again with something a little finer, and paint it. If the paint isn't too bad, just sand it consistently and lighlty with a finer paper, then prime and paint. I've painted half a dozen frames/ complete bikes in the past and haven't done too bad, and have no previous experience.