I just emailed you an awesome guide to do exactly what you asked, especially if you mean a DivX thats more than 700mb. Got it from a guy on another forums. basically it walks you thru how to cut the credits, and then recompress them at a lower rate, making the overall file smaller. hope it helps. if its not a movie you are looking to burn, you can try to use the guide to get an idea of how to recompress at a lower quality anyway.
-----Krugger