What I have done, with some success, is to create the Terragen scene and make sure I have more than enough foreground. I then take that scene into Paintshop Pro (not a big photoshop fan...too many buttons...) and I pull up the templates for Cyclorama and cut and paste the Terragen to work into the template. It takes a little practice for the seam area, I have to admit. Also, if you have more than enough foreground,and this works well for water or ocean based scenes, you can just lay it over the template as a new layer, cut out what doesn't fit, and call it good. Remember to save the new layer by itself so you don't overwrite your template.