I found loads of bat-mobile models on Google's 3d warehouse: http://sketchup.google.com/3dwarehouse/search?q=batmobile&styp=m&btnG=Search

Easy enough to covert .skp to .3ds then use blender to make it into a .nif. I haven't done much modelling so i don't know how usuable it really is though.

Edit: *Blushes* Aww, tweren't much of an idea, glad you like the Bobblebat idea

Thanks Stewb! I didn't realize there was an option in Google for serching 3d models!