Pretty sure AMD dropped opencl on XP, could be wrong though.
http://support.amd.com/en-us/kb-articles...pport.aspx
AMD Crossfire™, OpenCL, and AMD Eyefinity are not supported by the AMD Radeon™ HD 7900, Radeon HD 7800 and Radeon HD 7700 Series GPUs on Windows® XP. New technologies introduced with these GPUs are not compatible with the Windows XP (released 2001) operating system, and are designed to work on current operating systems.
http://support.amd.com/en-us/kb-articles...pport.aspx
AMD Crossfire™, OpenCL, and AMD Eyefinity are not supported by the AMD Radeon™ HD 7900, Radeon HD 7800 and Radeon HD 7700 Series GPUs on Windows® XP. New technologies introduced with these GPUs are not compatible with the Windows XP (released 2001) operating system, and are designed to work on current operating systems.