Did you ever figure this out?
The download includes files of the tank in .obj format. Make sure the IS3.obj file and the IS3.mtl file are both in the same folder. Open Blender and chose the "Import" and there pick the .obj option, the name of which I think includes the word "wavefront".
I myself used Blender on this model to separate the gun barrel, turret, hull and track from one another. But I was on a PC, not a Mac.