hum, you can check with dependency walker (http://www.dependencywalker.com/) that your OpenCL.dll file (in C:\Windows\System32\) provides the OpenCL 1.1 functions needed by pyopencl :

clCreateSubBuffer
clCreateUserEvent
clEnqueueCopyBufferRect
clEnqueueReadBufferRect
clEnqueueWriteBufferRect
clSetUserEventStatus

If not, then either the driver installation has failed, or it is not the good driver.
Otherwise ... I don't know 

Edit : you can check with GPU Caps Viewer if this GPU really manage OpenCL, because 2000 kh/s is what is currently made by the CPU alone.
The Geforce 9800 GX2 is if I'm rigth two 8800 GTX functionning in pair, not sure that they manage OpenCL.