Navisworks is a powerful applicatio nto bring together several file formats to view a project in pre-constrcution virtually. It is built on a video gaming engine, which compresses large files into a real time view to explore your project. The interface has been updated to be inline with the rest of the Autodesk produts, so finding your way around should be a quick learning curve.
Here is a link to more info. on Navisworks: http://usa.autodesk.com/adsk/servlet/pc/index?id=10571060&siteID=123112