There\'s a bug/feature in Visual Studio 2010 where you can\'t create a unit test project with the 2.0 CLR.
https://connect.microsoft.com/VisualStudio/feedback/ViewFe
It looks like Visual Studio 2010 Service Pack 1 will resolve this once it is released (see the heading 'Better platform support | Unit Testing on .NET 3.5')
You can get the Beta version with a Go-Live licence now...