Try a cooling fan blowing on the card.

yup,seems like the card is unable to run at stock clock (50/50 MHz),try underclocking it to 45/45..either edit the registry values or use some tool like Tweek for Voodoo!,see here: http://www.falconfly.de/tools.htm

Which CPU are you running? If I remember correctly some (I thought the latest) 3dfx reference drivers were causing problems on AMD K6-based systems. Try running an older or newer driver .

Be careful if you start 'messing' around with drivers by yourself. Older games, like DOS games, are going to search the GLIDE-files using DOS' path environment. Example: if you have the latest driver installed (for Windows) it will search in the Windows directory. But, if you copy the 3dfx-files directly into the root directory of the game it will use those drivers instead of the ones in the Windows directory. Anyhow, as long as you're not fiddling around with drivers manually this should not be such a problem.