If you have used 3dmax gmax is a cake. Gmax is most of the modeling and most of the animation tools max 5 had but free. They just simplified it.
The big drawback is it wont export to many things and can only import a few like 3ds mtl and obj files. I still have no clue what game 3dstudio shape came from .
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3dmax3,4,5 ,milkshape and gmax are the only 3dprograms i know that can export a working .mod.
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What u can do is model with truespace and export your finished work to 3ds and export to .mod through gmax.