of course you can rig in Gmax, you just need to get the right tools for it (which are easy to find). the ONLY thing you cant do with Gmax is render. as far as the software goes its capable of much the same as 3dsmax, you just need to find the right scripts/plugins. (of course things like character studio are gonna be Max only as they cost just as much on their own haha). look for something called SiegeMax, it is an add on for Gmax based for making it applicable with the title: Dungeon Siege. it should give you some handy new abilities. also, there are .xsi exporters out there too, if you look hard enough.