Pro Engineer seems to be ahead of AutoCAD in terms of 3d rendering and structural analysis. If you need to do analysis on an AC file, you have to export it to another program (can't remember the name) and then convert the file. ProEngineer comes with another program called Mechanica that is intergrated with it and doesn't require much messing about to run the analysis.
If you need more info, I'll get my lad to dig it out.