In the 12/8/08 Newsweek page 56-57 there is a good pic of a Pz IV used in the movie. I know they made a decent copy of a Tiger in Private Ryan, but are there any working Pz IV's out there or did they build a mockup?
In any case, the 2 page spread offers some good examples of shading on uniforms and vehicles.
Iy you look closely at the tracks in that picture, you can see there are two sets of tracks side by side. The outer set is a dummy that go with the dummy sideplate with the fake Panzer IV roadwheels and sprockets, while the inner set is apparently the real vehicle tracks. That sideplate completely hides the real vehicle wheels. It's a static shot, but I'd guess that the dummy tracks also turn when the vehicle moves, but they don't actually propel the vehicle. It looks like a good mockup and if it weren't for that big static shot in the magazine where you can look close at the detail, you'd probably be wondering how they did it.