Windows Forms as the Presentation Tier of a Three-Tier Application
A Windows Forms program can act as a standalone executable file or as the client portion of a two-tier system, similar to applications you may have developed using Visual Studio 6.0. Additionally, Windows Forms can act as a user-interface layer within a three-tier application. Using HTTP calls to a server that is connected to a database, Windows Forms are capable of acting as the front end to a powerful, data-enabled architecture that leverages the rich user interface of a client application with the advanced processing of an application server.
For more information, see Walkthrough: Creating a Distributed Application.