There are much longer more detailed ways involving editing the registry, running "devenv ..." command-line stuff, etc. This is by far the fastest and easiest way:
0.a. Make sure you have the ASP.NET MVC 1.0 Framework installed. I'm a dummy and still had the Beta installed and was surprised when the project wouldn't build. Then I realized my blunder.
0.b. Close any open instances of Visual Studio 2008
2. Click on the "NUnit Test Templates" link. Download the zipped file.
3. Unzip the file.
4. Run the installNUnit.cmd file.
That's it. Done. Enjoy.