First of all thank you all for your replies.
I must say that i'm not an experienced autocad user.
Maybe there is a solution in acad somehow.
I'm not really sure about how much detail i need in there.
The project is about a village on that mountain,
but the houses will be boxlike and the trees shperelike
so I'm not really worried about how "heavy" the whole scene will be.
(or should i???)
There will be closeups presenting parts of the village (not too close to the houses),
so, for now i dont want to limit my detail options.
Most likely i will not need full detail, but since i will have to create roads,
and flatten parts of it in order to place the houses, for now i want to keep the detail
and reduce it later on.
For starters i think i will try eliminating some splines and see what happens...
Here is the acad file, in case it helps...
http://www.photorealistic.net/terrain.zip