Just save your AI as a TIF or JPG and then import into Bryce Terrain Editor. Invert it, though, cause black is the smallest and white the greatest height value. Or you might try with copying it to clipboard and then pasting it into Terrain editor. I don't know whether that would work. Might, though. Or you could try TIFFER, but since the AI's straight B&W, I don't see much point in it.

-- erlik