There have been some questions in the Expression forums about product keys and apparent confusion as to which keys work with which products. The product keys are located behind the installation media (DVDs) in the Expression Studio box. This is what they look like:
Most of Expression Studio 2 uses a single product key to unlock it. The exception is Expression Web 2, which has its own product key. Expression Media 2 has two product keys: one for Windows and one for Mac. Using the Mac one on Windows will not work, and vice versa. The fourth product key in the sequence above is for Visual Studio Standard 2008, which is included with Expression Studio 2.
If you have a standalone (non Studio) version of Expression Media 2, you will find two product keys in the box: one for Mac, one for Windows.
I hope this clears up any confusion.