I\'m looking to introduce a unit testing framework into the mix at my job. We\'re using Visual Studio 2005 (though we may be moving to 2008 within the next six months) and
Visual Studio 2008 has a built-in test project type that works in a similar way to NUnit, but obviously has much tighter integration with Visual Studio (can run on every build and shows the results in a similar way to the conversion results page when upgrading solution files), but it is obviously not as mature as NUnit as it's pretty new and I'm not sure about how it handles mocking.
But it would be worth looking into when your team moves to Visual Studio 2008.