Key differences:

1) The rendering engine has been removed for GMax ( no big loss for us )

2) You cannot export models or save them in any format other than GMax native format. Plugins are 'licensed' by discreet to allow certain games to use the software for modding. There are plugins for Flight Sim 2004, Quake 3 and Combat Flight Sim 3...possibly others. This delibertae loss of functionality is the reason for giving it away. They make their money licensing hte plugins to provide game support.

As far as use for RTW goes:

Import - The CAS script works fine. You can import the models, play around with the mesh and get used to a user interface that is just about identical to Max. It has all the relevant Max tools for polygon modelling and is quite well supported with tutorials. It's good to learn on.

Export - You Can't. The stripping down of the Max core program has deliberately shut the door on most ways of getting models out of GMax, except through licensed plugins. You could get hold of the plugins, but you would STILL have to find some way of converting hte model back into a format Max could read, find someone with 3DS Max to import it, set up the materials, assign the skin modifier and allocate all the vertex weights. Phew.

In short.... learn the ropes on GMax. It's free, it looks and works like Max, and if you can master that, then you are going to be OK. Then get hold of 3DS Max to work on RTW