Terragen does not have a direct texture export option at this time. You would need to use a regular Render and set it up to be neutral for texture rendering as much as possible. That would generally mean orthographic camera, flat lighting (sun at 90 degrees for example), no atmosphere, etc. This will only work for things that can be represented in a planar map, so it would not handle complete textured models for example (unless they were essentially planar terrain models). You could apply your textures to a flat surface, render that to an image, then apply that as a texture map in your game engine perhaps.
- Oshyan