I have never used the export to encore command, but perhaps what it is doing is ready-creating an mpeg for you at a standard bit rate. I have exported uncompressed videos many dozens of GBs in size, and well over 1:30 hrs, and it's all fit on a conventional dvd. I guess in that case, Encore transcoded it and compressed it to a lower quality mpeg than it would normally choose to do so it could fit it on there.
So try simply rendering your video as an uncompressed avi and importing it into encore. When you finish setting up your dvd project, build the disc and (hopefully) encore will compress the video to fit.
Simon Bonner
youtube.com/simonsaysFX