Odd posterized colors on mac with ATI 9200

[napier]

Not sure what's going on here.  I'm running an LWJGL app on a Mac mini (ATI Radeon 9200) and alpha blended colors are showing up posterized (too saturated, and split into bands).  The same exact app looks fine on a Mac G4 laptop and all other computers I've run it on.

Here's a sample of what I'm talking about (top is wrong, bottom is right):

http://potatoland.org/images/mac_mini_posterize.png

The two mac machines have identical settings:  OS X 10.3, Java 1.4.2_05, display settings are the same (millions of colors).  I'm running .95 though I don't think this is an LWJGL issue.  

I'm guessing this has something to do with the card or some OpenGL tweak I need to do.  Has anybody seen anything like this?