OS X :: Diablo To LOD Scrambled Graphics

I have been trying to load Diablo II on a new 20" iMac with OS X v 10.5.1. I have attempted to load it a number of times, downloaded the patches and tried the "native" installer. The game appears to load properly; however, when we try to start the game it runs through the initial graphics (ads) and then shows a scrambled diablo page (looks like large square puzzle pieces placed in the wrong positions on the screen) and you can only escape to end the game form that point.