After you click Load IRender, do more IRender functions appear at the bottom of the Plugins menu? If so, then the application is loading, but the toolbar is not visible.
If this is the problem, try this:
It's a problem we've run into since SketchUp 8 was released.
We've found that you can fix by doing the following:
Using the SketchUp View/Toolbars menu:
See if "IRender_nXt" is checked.
If it is not, check it, and see if the IRender nXt toolbar appears.
If it does not, on the Toolbars menu, uncheck "IRender_nXt", and toggle the Large Buttons checkbox once and close the menu.
Then go back to the Toolbars menu, toggle the Large Buttons checkbox once, and check "IRender_nXt".
Then the IRender nXt toolbar should appear.
Once we get it to appear in SketchUp 8 once, it seem be OK from then on. If it ever doesn't appear again, you should just need to check it on the View/Toolbars menu again.
If that is not the problem, load the SketchUp Ruby Console before loading IRender nXt and send me any messages that display to: al.hart@renderplus.com