I have been using the old terragen for a long time with max and it all integrates quite well with some help from a few plugins and some custom software ive written. I can export a terrain from terragen into max, create a camera move in max and export it as a script for terragen to render the backgrounds. Im thinking of buying tg2 and the animation bit but does it have anything built into it just now for integration with 3d apps and max in particular.
You may find this thread to be of interest: http://forums.planetside.co.uk/index.php?topic=172.0
We expect support for more 3rd party applications to improve significantly by the time the final product is ready for launch.