I agree with Chimpy, if the rust is so bad then there is a lot of metal that has been eaten away making the rims weaker.
Wire brushing is not the best way to remove all the rust as even the tiniest black spot left, is rust and it will start again the only way to be sure is shotblasting. Painting is a temporary solution only even after shotblasting one slight chip or scratch and the rust will have somewhere to start again.
If and I say if !! there is no chance of new rims and I am reasonaby sure there is a good chance of getting new rims then get them shot blasted and assesed to see if they are still ok and have them enameled/powder coated.
Have a look here
http://www.northwestenamellers.co.uk/However if your rims are that bad ...what state are your spokes in??
Regards Witch