Enabled "Low performance" in the options this will reduce the load on the CPU. Then click more in the options check low res textures and slide the detail sliders to the left. Ensure Advanced Effect is unchecked. try changing the fog to Vertex or Emulation.
If the game still runs slow look for utils that can change the global settings of your video card. If its Intel Graphics there is a strong community that release custom drivers to improve things so that could be an option too. (phdgd site is dead and they moved to facebook so be careful when downloading anything from untrusted sources).