Aaron Hallberg has a written a great post on one of the new extensibility mechanisms we've added to the Microsoft.TeamFoundation.Build.targets file that forms the backbone of the msbuild process (it's imported by every tfsbuild.proj file and contains all of the targets and properties). Aaron shows you how to have a different target called for each of the projects and solutions that you build, which allows for greater flexibility in hour your projects and solutions are built.