Download the latest 226 patch.
Then start the game in safe mode (the game should have installed an "Unreal Safe Mode" shortcut in your start menu). Go to the options menu and choose "advanced options". In the "drivers" tab and chose "3dfx Glide in Windows" and quit the game. When you restart it you should have Glide rendering.
In response to your future question, Glide is dark because it doesn't use gamma correction. Give Direct 3D a go if you like. You may have to experiment a bit to get everything right.