Lionel Oliver has an amazing site documenting his experiments metaling and casting metal. He shows how to build a variety of furnances from a simple charcoal furnance out of bricks and dirt to more complex propane furnaces. The best part is he does this all in his backyard.
Once you can melt metal you can start recycling old things like aluminum cans or lawn chairs and forming real tools and parts.
Lionel even built an entire gingerly lathe using his metal foundrys.