Rose, have you tried updating your videodrivers?

Diamond still has drivers for their old videocards: http://www.dmmdownload.com/legacy.php

I think you need the "DIAMOND STEALTH S5XX WIN9X NT4 2K DRIVER" one.

I'm not sure if this will fix the problem, 'cause if these drivers do not support DirectX9, the problem will still remain.

Finding a somewhat younger PCI graphics card that is supported by Beyond Divinity isn't going to be easy... For instance, I think nVidia stopped making PCI cards after GeForce2.