Under .NET, the interpretation of what is and is not a dialog is largely dependant on the user interface you choose to use on it. As was mentioned before, a modal dialog is something that requires the user to finish his or her interaction before continuing with the rest of the application. Therefore, dialogs become less and less useful as they get more complex. You must make very careful decisions about what functionality goes into the application's forms and what goes in its dialogs.
Modal and Modeless Dialogs
A dialog can be created in the same way as a form, by dragging tools from a tool palette or by laying out components by hand. The Form class has a property called Modal that will cause the form to be displayed modally ...