I am familiar with nunit for unit testing of the business layer however I am looking now to automate the test of the win forms gui layer.
I have seen watin and the
As far as I know, White is an abstraction layer over the top of Microsoft's UI Automation framework. I have written a similar layer that we use internally on our projects and it works great. So White would definattley be worth a look
Microsoft have released the source to UI Automation, so if necessary you should be able to debug right down the whole stack if necessary.
The really cool thing is that with licence cost, you can scale up and run as many machines as you like for execution.
We run inside VSTS and link our results to requirements, but you can use c# express and nUnit and get first class tools and languages for little to no cost.