Download a bit rate converter to give you an idea as to the bit rate required for a 2 hour DVD. I recall using something like 4.5-4.7 VBR (Vegas 4.0e) to get a 2 hour show onto one disk. The AC3 audio option takes up less disk space than .wav and give you a bit more room for video. Once you find a setting that works for you, save it as a preset.
Hope this helps.
Ken
the Screen Skins guy