There is a folder named SDK under Team System Web Access installation directory, which includes a reference for developing work item custom controls and a sample project with a number of custom controls inside.
When you open custom control sample project ( [TSWA] \ SDK \ CustomControlSamples \ TSWebAccess.CustomControlSamples.csproj) in Visual Studio 2008, you will see that some files are missing.
This is caused by a mistake made during the deployment process of the product. It is possible to remove the missing file references and make the project build successfully as a work around. If you want to have the corrected project, you can find the zipped project files below.
Sorry for the inconvenience.