Without seeing the content of the .obj or knowing more about the provided model, I can only make a few educated guesses.
The "hard part" the creator did included the actual modeling, the UV mapping for texture projections, the texture painting/creation, etc. All that work should still be preserved in the .obj data and .png files so long as there are entries that match up vertices to uv coordinates. Try applying the diffuse texture to the model and see if it's already projected correctly onto the geometry.
(incidentally, you DO have textured-view turned on in your viewport, right?)
Edit: forgot to mention, the .mtl file might very well have the various texture assignments stored in it, you might skip a few steps by applying that material to the mesh.
Edited by BCullis, 05 February 2013 - 01:01 PM.