You might have too much detail on your model, this can range from simply too much 3D detail, i.e. showing stuff like threads, bolt holes, bolts & nuts, etc. or when you want to show surface details like bump maps, texture and so on.  Lighting also eats processing power and eventually if you ask too much of the machine you'll get either a freeze or sometimes the notorious Autodesk error message or even the BSOD.

 

Generally a 3D file of that size is actually on the small side, my files tend to be up to 100 mb +.  The machine I use runs Win XP, Nvidia Geforce 8600T g/c with 512 mb on board ram, 2.8 Gig CPU and 4 Gigs Ram and it will take about 12 minutes on a 80 mb file with lots of detail to render.

 

Hope it gives you some insight.