U should read about "narrow" and "fat", "obstacle avoidence" and "pathfinding". Did u thought a 3d engine handles "correct" movement of models by itself ? If so, no, they wont. ^^
Take a look at Superku's pathfinding.c included in the goodies.zip, if its up to easy non-cost pathfinding.
Edit: Ull find a simple and good oa at bottom of this post:
http://www.opserver.de/ubb7/ubbthreads.php?ubb=showflat&Number=428514