Well, it's pretty clear that I won't be getting much help (probably because RasMol will probably never be used by anyone else on these forums), but for the interested I've managed to compile it in the seemingly hidden 16-bit colour mode and made some progress (after much toil and modification) with no errors during compilation. But now, instead of getting the "No suitable display!" warning, I get a "Graphics Error: Unable to find suitable font!" error. In the source files there seem to be two fonts (Helvetica and "serf" -- ?). I found and installed a helvetica TTF font and, although AbiWord seems to recognize it, I had no luck running the program. I haven't yet tried installing the "serf" (serif?) font yet (that's next), but I doubt it'll work. I've also tried changing the font names to verdana (I'll try the more generic arial in case something weird happened), but it's not looking good.
I also found a newer version of RasMol which seems like it should work better (all struct fd_set's were already changed to simply fd_set and the 16-bit mode seemed more supported in the source files), but it gives me even more errors which I haven't tried to attack yet.
Just for the interested (if there are any).