Tnx for suggestions!
@NitroLiq:
yeah, I just found out about that thing and it just what I need.
The only problem is, that when I convert displ. map into polys, it has a height of 0 (or at least I think so;when you look it from the side view, it looks just like a plane), so I have to scale it when it's already converted (which is not a problem). Anyone know perhabs why?