How to organize UI testing depends on how you design the test cases.
Automating Windows Forms application in unit test level can use TDD framework, such as NUnit; or use BDD framework, such as NSpec.
Automating Windows Forms applications in functional testing level can use White, CodedUI, or even directly using Windows Automation API 3.0 (UI Automation and MSAA).
Since all these stuffs mentioned above are technologies rather than solutions, it's better to build some fundamental test automation/scripting frameworks based on these technologies before you start to write automated tests.