Hi Dmitry,
instead of changing the actual main program every time you want to test a form, it might be better to add a new empty project to the solution, add the other project as a reference, copy over the main program and make this debugging application the EXE that the debugger launches. Otherwise it's almost guaranteed that at some time in the future you forget to change the main program back to the original form before you make a release.
--
Christof