Removing Rust from Cast Iron Pan

Cast iron pans can be cleaned with a homemade paste of course salt and cooking oil. Rub vigorously with a dry cloth or a plastic scrubber and do not use any water.

http://www.wikihow.com/Remove-Rust-from-a-Cast-Iron-Skillet
After you remove the rust, I assume you want to use this for cooking; you will have to go through the steps to 'season' skillet, once seasoned, Do not scour or wash with soap again. Treat it as a delicate cooking utensil and never put it away without wiping it lightly with an oil. [I give mine a light spray of Pam, then wipe almost dry, then cover with a sheet of wax paper to prevent dust from settling.
http://www.howtodothings.com/food-a ... w-to-season-a-cast-iron-skillet.html