Before you can use Code Metrics Viewer within Visual Studio 2010, you also need to download and install Code Metrics Power Tool 10.0. The Code Metrics Power Tool 10.0 is a console application which is available at Microsoft. The download can be found at: http://bit.ly/lVH1Aa
The extension comes up with it´s own options page, where you can specifiy the installation path of the Code Metrics Power Tool. Please have a look at the Readme-file provided together with the Code Metrics Power Tool 10.0 to find out the installation folder (might be: <Program Files>\Microsoft Visual Studio 10.0\Team Tools\Static Analysis Tools\FxCop). The specified path shall not contain a filename (the extension will add the name of the executable). Consider that there is a difference in the <Program Files> path between 32- and 64-bit versions of Windows.