A WMB file is a game level, so it will contain 3D models as well as textures. However, WMB is the compiled level, not the editable level you would work on designing. I misread this part, and assumed you meant WMP, which is the editable level.

As WMB, it would be much more difficult to extract models and textures from it. txesmi's script, if I understand it correctly, would allow you to open a WMB and extract models/textures as you need, but if you are not familiar with how the engine works, and how to run scripts, then that might look intimidating.