For the Refinishing of tub and tile, check out : http://www.ximbonder.com/products_detail.asp?id=48
Also comes in a spray can as well. Also recommend using : http://www.ximbonder.com/products_detail.asp?id=53
Use that Etching solution prior to any kind of painting.
Now. With all that said. Is your tub porcelain? I am just assuming it is. Also, do you want something other than white?
I would actually recommend using the etching solution, and then two coats of a Sherwin Williams Epoxy, Duraplate 235 NSF. I feel the Duraplate is a better product than the TileDoc, but the TileDoc is probably a little easier to use. Got any more questions, shoot em my way. It's the company slogan.