The path containing the root folder: OPENCV_DIR is c:\opencv\build\x86\vc10. This of course would be "slightly" different depending on the platform, drive installed and the compiler used. The key is as it relates to the essential parts of the package. That is, the include folders and the library folders. The two mentioned are actually up two folders from the bin folder. This means the environment variable mentioned in the install instructions is quite inaccurate.
Would anyone please offer a correction? I downloaded ver. 2.4.5.