Number of exported texture stages
Sets the number of texture stages the driver should report to the application.
Max Local Vertex Buffer Size
Sets the maximum size in bytes that can be used in local memory to store vertex buffers.
Max AGP Vertex Buffer Size
Sets the maximum size in bytes that can be used in AGP memory to store vertex buffers.
Default Vertex Buffer Size
Sets the default size in bytes for vertex buffers.
Max Matrix blend
Sets the number of matrixes that can be used for vertex blending.
Max Matrix Streams
Not sure, but it probably sets the number of matrixes that can be used for in a Matrix stream.
Hardware safety level
Not sure, try it :)