I didn't try the demo but if you are using Advanced Terrain you can use:
position object myobject,object position x(myobject),position object y(get terrain ground height(terrainobject,object position x(myobject),object position z(myobject)),object position z(myobject)
DarkAI doesn't concern itself with the Y value, as this would complicate the AI to a whole new level.
If you are using a matrix just replace get terrain ground height with get ground height. If you are using an object, you'll have to do a raycast downwards from the bottom of the object or find another way to handle it.
