The production version of FxCop can be obtained through the Microsoft Download Center. As of this writing, the latest production release of FxCop is version 1.36 and is available at http://www.microsoft.com/downloads/details.aspx?FamilyID=9aeaa970-f281-4fb0-aba1-d59d7ed09772.
The code analysis features of Visual Studio Team System 2008 Development Edition most closely correspond to those available in FxCop 1.36. The API for developing custom rules is the same in both. However, Visual Studio includes additional rules out of the box that are not included in the free FxCop.
FxCop 1.36 will run under and analyze programs written for .NET Framework versions 2.0, 3.0, and 3.5.
Everything that you need to develop custom rules is included with the main FxCop download. While the API is officially referred to as the FxCop SDK, there are no separate SDK files to download.