If it is your starter, then it's probably the brushes in your starter.
In a pinch, you should be able to get the starter to work by having someone tap your starter while someone else cranks the engine.
It's an old trick that I used to do on my old chevy. You can get the brushes to move a little so that the starter will turn. However, you really need to get the starter replaced. I just replaced mine. Search around the forums for more information about it.
Good Luck!
