Nvidia has an OpenCL beta download available. Nvidia's OpenCL driver will only allow you to run on Nvidia devices. You must register as a Nvidia developer to gain access. For more information
http://www.nvidia.com/object/cuda_opencl.html
AMD has an OpenCL beta download available. AMD's OpenCL driver will only allow you to run on AMD CPUs. They will be adding support for running on ATI GPUs towards the end of the year. You must register as an AMD developer to gain access. For more information
http://developer.amd.com/gpu/ATIStreamSDKBetaProgram/Pages/default.aspx
