Add an interface to the project which contains the executable file.
Add method that calls WindowsForm. Naming this method based on the convention will make dicon file setting easier.
Use Seasar.Windows.Attr.TargetForm attribute to set form to a method.
ID is just an example of a argument. Value of the argument is set to the form ID property. In other words, define a property on the form with the same name as the argument so the value will be set. Datatype of the return value will be either void or DialogResult.
Set the project of the executable file to the application execution class.
This can be done by moving the Main statement from the default form created when the project is created. Project startup object should, also, be changed to this executable class.