There are many tools and libraries available that can automate WinForms testing, ranging from open source solutions like White to the expensive commercial solutions such as HP QuickTest Pro. There is also the UIAutomation namespace in .NET if you want to roll your own automation framework. But the real cost of automation is in the time and specialised skills it requires to implement. Maintainability is also one of the most important aspects of automated test design; you dont want to expend excessive resource keeping the automation assets current with your application. There are also lots of factors influencing the decision to automate which will be specific to your specific application and organisation.
Your best bet will be to do some more research on the subject and check out some of the specialised testing sites such as http://www.sqaforums.com.
