As I see it, N-unit and White are separate entities. If you are working with Visual Studio then you need to primarily do the following:
1. Create a new project of type Class Library
2. Add Nunit related references [nunit.frameworl.dll]
3. Decorate your test classes and test methods with the keywords [TestFixture] and [Test] repectively.
4. Now you should be able to open the dll in N-Unit