Older versions of Demul (I think 0.5.3) has two different OpenGL plugins, and a Direct3D plugin. The newest version (0.5.4) only has the Oglv3 plugin for graphics. All the plugins Demul uses are provided with the emulator itself, and IIRC, can't be downloaded anywhere else - there aren't any other plugins anyway. Plus, it seems that the plugins are version locked, meaning that you can't use plugins from 0.5.3 in 0.5.4, for example.
When was the last time updated Nvdia's ForceWare drivers?