Frank, I need to clarify something before I continue. I'm blocking out my image from Terragen into sections of the TG2 screen, so I'll have more than one render from the same screen in TG2. I'll need to reassemble these in Photoshop. This should be okay, right? To be clear, I'm talking about splitting up the render in TG2 to help with render times, etc. But, the only thing I'm planning to do in Photoshop is reassemble the rendered images from TG2.
I'll probably use Photomatix for lighting.