Yea nice render. i definitely will use that dirt on my cars too, but the reflections are very wrong. Use the same picture for the reflections too, but I think the problem is Blender for that.
please, just don't use the first tutorial, it's a shit... http://video.google.com/videoplay?docid=6738085731963530700 - this is one of the best(or the best) rim tutorial what you can find, the quality isn't the best, but you can see what is he doing