Check out this useful macro for visual studio 2005 dependent (nested) items. Useful for breaking up large classes into partials when refactoring doesn't make sense. I found it useful when you want, for example one integration test class per implementation class and the test class is getting a bit large.
Source:
http://www.delarou.net/weblog/PermaLink,guid,a81a2d9d-02de-4fe1-ad8d-ee2fee97cf20.aspx
Visual Studio .NET Macro for nesting project items
This macro enables you to nest project items inside Visual Studio .NET. Until now, there is no easy way to nest project items through the Visual Studio IDE, you can only do it by manipulating the project (.csproj or .vbproj) file and adding the DependentUpon element.
Inside the IStaySharp.vsmacros file there is a macro called 'Create Dependency' which allows you to nest two selected items. I have even created a video (672,18 KB) to illustrate how to configure and use the macro.