To create a new vehicle for the game you need some things
a) a copy of 3ds Max 8 or 9 (or Milkshape 3D, not recommened though since it is much more difficult to export vehicles etc with this software)
b) the official exporter plugins for the above software (or the inofficial plugins for Milkshape 3D).
c) some basic skill in 3d drawing
d) a lot of patience since it involves a lot of try-and-error before you get the hang of it.
e) a uvmapper (comes built in with both 3ds Max and Milkshape 3D, but there are several easy-to-use uvmappers to be bought or downloaded for free (lithunwrap for example).
f) a paint software to create the vehicle skins with. You can basically use Windows Paint to do these, but Photoshop or Paint.net is better recommended.
That´s basically all you need to create new vehicles for the game.
There are several tutorials on how to export and create vehicles (with 3ds max) floating around online, but 99.9% of these are written in Russian and if you don´t understand this language, you are basically on your own.
I´ve no experience whatsoever in 3ds Max or exporting with that software so I can´t be of any assistence with that software.
Here is a link to where you can find some tutorials for 3ds max written in English (last post in the thread)
http://www.digitalmindsoft.eu/forums...n-of-war/page3 . Hopefully the download link still works.
~Zeke.