Rage Pro opengl problems :(

I have been trying to get opengl to work properly on my Rage Xpert 98 now for months but still no luck. Ok here's the problem:

I run Starsiege and go into options, where OpenGL using Rage pro is selectable. I switch to OpenGL. I go back into the game and the framerate has dropped to unacceptable levels Also some areas of the screen such as thin green frames around menus flicker.

I have tried downloading the latest drivers for my card but that just adds graphics coruption to my problem. I am running in 16 bit colour.

Dynamix (makers of tribes) have been no help, neither have ATI - Help me out?

Thanks.

By the way I have a Pentium III 450, 128 ram and Windows 98.
HELP!