Every steel rim I have seen is chrome plated, so if you are seeing rust, it has probably bubbled through the chrome. Depending on how bad they are, you will never get them close to where they were when new.

Also, since you don't know the difference between steel and aluminum, just to make sure... When you say rim, what do you mean? I only ask because some people refer to the whole wheel as a rim.

But the bottom line is: Unless the wheels have historic value, I would suggest replacing them... You will be much happier with the lower weight, and braking capabilities (assuming rim brakes).

If you are hesitant to buy new wheels, I can understand that. Could you post some good pictures of the rusted area(s) as it could provide a better point of reference.