I have an Nvidia GeForce8400GS grpahics card with which I am trying to mine for fun and experience. I know , I know I wont get good performance , .... but atleast it has to work right. So first I installed http://www.nvidia.com/object/win8-win7-winvista-64bit-320.18-whql-driver.html and when it still didnt work I installed https://developer.nvidia.com/cuda-downloads but it still says no opencl devices found. Could someone please help me out?
Well since you install CUDA then you need to use a CUDA based miner. I have no idea if Guiminer used Cuda or not, but I'm pretty sure Ufasoft does.
Also according to the Mining hardware comparison chart it will hash slower than your CPU.
https://en.bitcoin.it/wiki/Mining_hardware_comparison
Good Luck and have fun,
Sam
Edit: OpenCL is for AMD GPU's by the way.