Thanks anyway JeffMOD. It seems Terragen 2 can do so much more, what a shame the script doesn't work with it! I have found a workaround of sorts; Load a near empty map into HL with just just distant geometry you need, and set the screen resolution to 320x240. It's close enough that I was able (with a little bit of photoshop skill) to blend screenshots of the geometry in with the skymaps. Not ideal but it'll do me for now.
Very helpful, thanks JeffMOD. What if you wanted to make an urban setting, with faraway buildings in the skymap instead of mountains. What would be the best way to do that?
EDIT: Forgot to say, yes they freakin' kick ass!