This article is the result of a prototype I completed late last year.  The prototype investigated if and how Windows Forms in .NET could be invoked from a Java application written using SWING.  This approach is helping customers today to migrate to a .NET Windows Forms / Smart Client strategy without having to perform a complete rip and replace of their existing client setup.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnbda/html/SWINGWinFormInterop.asp