MySoft, regardless of the hardwares vendor, if you're using the built in XP or Vista driver, you will not have an OpenGL ICD, as these are stripped from the driver before they are sent to ms to be put on the disk, why this is i don't know, Microsoft are probably still touchy on the subject that OpenGL out classes it, and the only reason why more don't use it is because its a little more complex to use then the evil DirectX
This in turn falls back to using the OpenGL 1.0/1.1 ICD installed with windows (opengl32.dll) vendor specific icd's have a part of the owners name in them usually.. etc nvoglnt.dll and atiogl.dll
hell you can even use all of the features of Dx10 on XP using OpenGL (Geometry shading included!)