To remove a really stuck bolt, get some good penetrant (nothing works like PB Blaster) and a propane torch, available at your local home fix-it store. You can also use a butane torch, it's just a little cheaper and easier to go with the propane.
Safety Tip: Be extremely careful with an open flame! Never use an open flame near a fuel or brake line. Flammable fluids and open flame don't mix. The flame will burn anything rubber it comes into contact with, including trim, seals, and wire sheathing. It will also ruin paint instantly.