After struggling around for some time now and having several posts of installation failures (in the comments or at StackOverflow) I picked up the idea of Timur and managed to get the project template for NUnit and ASP.NET MVC 3 put together into a Visual Studio Extension. The benefit is, that there is no installation which does registry changes but delegates the merge process of needed registry settings to Visual Studio. This is done via a package-definition file added to the extension. If you want to dig deeper into that I can recommend following to read:
Both articles are describing the starting process of Visual Studio and the registry merging well.
At current state the extension is only available for Visual Studio 2010 Professional and higher editions. This is only while I am not aware of the fact if it is possible for lower editions to run extension. Maybe I will research about that later and eventually open the extension for all possible editions.
You can now find the extension under following download-link: ASP.NET MVC NUnit or via Extension Manager in Visual Studio.
Functionality is the same as before - ok there is not so much to improve or change ;-)