The vast majority of functionality in VS.NET is implemented through packages. The Visual Studio Integration Program enables you to write your own packages, which means that your project types, editors, and designers effectively become peers of the built-in project types. VS.NET extensions built as packages are first-class citizens within the IDE. The main role of the IDE itself is to be a shell that hosts packages and enables them to exchange services. For more information on how to obtain the VSIP SDK, see http://msdn.microsoft.com/vstudio/vsip/vsi/default.asp.