WoW graphics distortion

[azazthot]

After upgrading to 10.5.5 i got grafics distortion playing wow. It begins after a couple minutes of playing and becomes worser. After resetting to default setting it becomes ok for another couple of minutes and then again...
Everything is marvinized.Geforece 8500gt with efi string. The rest of OpenGL apps (googleearth etc.) working perfect.
I reinstalled wow twice...
It work ok un WMware fusion vista, but naturally slowly.So it is irritating to reboot into vista just to play.
Where should I check? (i guess that it is an opengl issue, but...)

Thanks.