Nels Bruckner, TRIBES Project Manager for Dynamix, sent in this explanation of the bug in the recently released Starsiege: TRIBES 1.6 patch that's plaguing 3dfx card owners (story):

Arg! We let an obvious one slip through in the 1.6 patch of Tribes. The specific problem is with user created art (reticles, skins, etc.) and Voodoo configurations with more than one TMU. User created art will show up as either all black or black and white or as other funky looking combos... basically totally wrong. We have the problem fixed, we will get the patch up ASAP. My apologies for this obvious error.

People seem to be liking the OpenGL support though! :)