Is it possible to use AutoCad or Maya to model weapons, vehicles and bipeds and export them to MAX? I heard Maya was good with bipeds, and AutoCad has some ok modeling abilities.

Ok, before any more of these " Can ____ program be used to make stuff" Ask yourself a very simple question. Does it export to a file usable by either 3ds Max or Gmax? For both of those the answer is yes. Although Autocad you'd just save teh file and import it into 3ds.. Its just a buncha splines...

Sorry AutoCad you have been voted off the island.

So how good exactly is Maya good with modeling bipeds?

I've heard Maya is easier with modeling organic things... I wouldnt really know though...

maya is an extremely good and complicated modeller just look at videos on youtube that and zbrush are very good for bipeds and such thats what they use to model bipeds from 360 games not sure if they modelled bipeds for h3 in it but it is a very good program to my knowledge but ya gotta pay money for em but it would definatly be on my list for things to get for my comp if i couldnt put em in halo id make movies and such lol why not try it if ya have it

Well, AutoDesk has this Maya Personal Learning Edition (PLE for short) and its free, idk if it can export to 3ds max or has Max Script, but might be useful.

h3 was made with 3ds max (i saw a guy making a valhalla base on 3ds max lol)....renember that bungie sticks to 3ds max lol

autodesk also has this program called mudbox that is very good for modeling bipeds but im not sure if you can import into max because it is a very different stlye of modeling. and even if you could it would be extremely high poly.