There's a free (older) version available, you can download it from their site
However, I don't know much about how to work on that though.
50 euro's is not much, 3DS Max is much more expensive.
After making the polygons in Z-modeller you need various other programs.
You need something to colour your models too (like Adobe or PaintShop Pro).
After doing the polys and smacking on the color, your model is finished and you'll need to import it into GTL.
Biggest problem in GTL is that all original files are encrypted
So really nobody does know exactly how to work out any physics.
I mean, you wouldn't want your freshly produced Lambo Miura to behave like a Ford Falcon....:p
Meanwhile some add-on cars are available, so a tutorial might follow.
Good news about this is, that all the physics-editing is done by WordPad, which is a standard-delivery on all Windows editions.:roflmao:
Just wish we could see the original files in Word-Pad, all you get is jibberish.
We could learn mighty much from those ones!