I'm in the process of adding ASP.NET MVC to an existing ASP.NET WebForms app in Visual Studio 2008. One of the neat features of an ASP.NET MVC app is that when you right click on the Controllers folder in the Solution Explorer the "Add" menu item has a "Controller..." menu item on it and right clicking on the Views folder causes the "Add" menu item to have a "View..." sub-menu item on it.
It took me forever to work out how to get my WebForms app to also show those menu items. It turns out that you have to edit the .csproj file for the WebForms app and find the section that reads:
The to that add the following GUID:
Such that it now reads as follows: