During SDK installation, the environment variable PIXELINK_SDK_ROOT was created for you. It is set to the root directory of the SDK files.
For example, if you installed the SDK to C:\Program Files\PixeLINK, PIXELINK_SDK_ROOT will be set to "C:\Program Files\PixeLINK".
Checking the Value
You can view the value of the environment variable several ways. Two easy ways are:
1) From a command prompt (cmd.exe) (also known as a DOS window)
2) In the System Properties dialog (Windows Key + Pause/Break, or right click on My Computer, then select Properties, or, under Start, Settings, Control Panel, Settings) go to the Advanced tab, and click on the Environment Variables button.
You can see here how to use it to configure your Visual Studio C/C++ project.