Not complicated, but very tricky. Not only beginners having problems with collusions.

You need any help? Just getting started with GS?
Go here: http://badcom.at.ua/
Feel free to ask anything at formspring! My profile is KMRobert

well what if i say i'm just starting with GS and i need some help?

You need to go through workshops, before asking for help. If I'll help you right now, there will be no sense, cause you wouldn't be able to understand.

@ Mythran

in the entity's properties window, you have a list of flags
such as transparent, nofog, nofilter etc.
you also have a flag called "polygon".

If you click this flag for static entities, they will behave 'as blocks do'.
I don't know if this is what you want, could be a misunderstanding,
but it involves no programming. just a single flag

it is actually the same as some users already said

Well that is what i want, but the only problem is that it won't work...

The player is supposed to climb walls when you press ctrl, and it works
great on block, but in the terrain when you press ctrl he tryed to climb,
it seems he believes it to be a wall, the player just walks over a tent
as if it had no height...

And in the block next to the tent everything works perfect..

Here is a demo and you'll see what i mean:

http://www.2shared.com/file/COfOml4Y/Demonium.html

Thanks