Before you can encode your video in MPEG-2 format you'll need to know what amount of bits are available to you on your DVD. This involves figuring the amount of video you have and dividing it by the amount of space left after audio and menus. The easiest way to accomplish this is with a bitrate calculator, although it may require several uses for DVDs with both a main feature and extras.
This is the fifth guide in the Basic DVD Authoring Project. If you're not familiar with the series you may want to start at the beginning. It should also be useful as a general guide for using a DVD bitrate calculator.
Basic DVD Authoring Project guides: