How can I?

I do have a calendar with a multiple schedules (user 1, user 2 and user 3), and I wanted to display a confirmation message to the end user in he decides to move an event from user 3 to another user. ( I am using almost the same form that comes with calendarcontrol sample to add/edit event, and I prefered that this form will be loaded every time a user try to move an event from 1 user to another user within the calendar)

please tell me how?

Thank you