Just did a quick Google search for it... they had it over at AH-Terrains but that page seems to be down now. Maybe NHawk still has a copy of it somewhere...?
There seems to be another utility out there called BMP2MAP, but it's for creating Quake maps, so be careful to make sure it's the right one.
Anyway... IIRC, BMP2Map would let you import a greyscale elevation map, and based on certain settings that you put in, would assign different tiles based on slope, elevation, etc. This just might be the thing you're looking for.