Your link is wrong, the website has an old certificate so most browsers won't accept it with https in the address. The video inside the thread is too old so it's not available.
The link is this one http://forum.dark-omen.org/singleplayer/help- … 41-t1653.0.html
You say the screen is flickering in Warhammer Dark Omen with a Pentium M / 256MB ram / ATI Radeon 7500 AGP. You can try running dxdiag and see if it says anything useful. On the screenshot with the crash in the ati property page, there's a message about directx 5, while your graphics card is a directx 7 card. You could try reinstalling directx or installing at least directx 7.
You have an lcd screen so it's not an issue with the refresh rate. It's not actually flickering, it's something with the rendering because of drivers or the graphics card.
Is there a native directx version of the game or is it only 3dfx/glide ? If there's a native one you should use it, not the 3dfx version. If you want to use Dgvoodoo, use Dgvoodoo 2 not 1, but I think you need a recent version of directx so you'd have the same kind of issue with an old directx.