cant run OpenGL in Starsiege: Tribes - help please

ok, i have a ATI Rage Pro and i cant seem to run Tribes with OpenGL. the game run fine in software but in OpenGL its distorted and choppy. i have downloaded the latest drivers for the card and it doesnt seem to help. anyone have any suggestions?

the same thing happens on another of my computers as well but is not choppy, just distorted. yet it is using a Hercules 3D Prophet video card. i have tried everyhting i can think of, maybe another head in the problem will help fix it.