Hi!
Is it possible to use this (http://www.3dm3.com/modelsbank/model436.htm) or this (http://www.3dm3.com/modelsbank/model421.htm) model in your AGS game?
Is there any plugin that allows me to use that kind of 3D models.
Short answer: no.
For the long answer, we'd have to know what type of game you want to create. A bit more info.
The two 3D related AGS things that come to mind are the 3D characters plugin(I've never looked at this), and the AGS 3D plugin/module.
I haven't looked at them much, And you haven't supplied much info, so I'm not sure how helpful those things would be... :-\
AGS could possibly be 3D, in the same sense that the original Doom and Castle Wolfenstein are 3D. It's a pseudo-3D, but I'm not sure that AGS has that capability built in.
To do it, you'd have to recreate the painter's algorithm (http://en.wikipedia.org/wiki/Painter%27s_algorithm) or figure out how to do z-buffering (http://en.wikipedia.org/wiki/Z-buffering). You'd be recreating the 1d Tech 1 (http://en.wikipedia.org/wiki/Doom_engine) engine to do it, I think.
It'd be interesting to see if it can be done, because then the engine could be expanded to creating FPS games.
It depends on what you meant by "3D".
If it's pre-rendered 3D sprites or backgrounds it is definitely doable and straight-forward. (So the answer is a 'yes' if you manage to use said models this way.)
If it's in real time then AGS is not primarily designed for such things. However, we have a couple of modules and plugins that may achieve this to various extend:
Easy3D module (http://www.adventuregamestudio.co.uk/yabb/index.php?topic=26130.0)
AGS3D module+plugin combo (http://www.adventuregamestudio.co.uk/yabb/index.php?topic=29419.0)
Character3D (http://www.adventuregamestudio.co.uk/yabb/index.php?topic=23400.0)
Panorama3D (http://www.adventuregamestudio.co.uk/yabb/index.php?topic=38512.0)
Note that some of these haven't been updated for a long time (and some are recent additions, like the panorama one) and they may not be directly compatible with newer versions of AGS.
Personally I'll say if you're really seriously about making a real time 3D game AGS is not a good choice though.