As previously mentioned, nXt render functions well with auto bump applied to materials in SU 7. The beta version of nXt render loads into SU 8, however when I right click on a material to set attributes, nothing comes up on the screen ... so although the beta version loads into Su 8, material attributes can't be set. Since I use this frequently, I do my modeling and rendering in SU 7.
From another thread, but can't provide link as URL not appearing in browser
"There is currently not a Beta version released, because we have had such a hard time getting a good stable version out which works with SketchUp 8. We couldn't take a chance that new potential users would download the old stable version, have it fail with SketchUp 8, and then never try IRender nXt again.
We will start issuing Beta versions again soon. In the meantime, if you are not using the old Beta Versions, you should remove or rename the IRender_nXt_Beta folder from Program Files."
I would suggest downloading latest version see thread "IRender nXt / nXtRender - new stable version - JJ06"