popups-how to make them modal?

himali

I need to create different popup windows in a course and make them modal, so that user cannot click on course window unless he closes the popup window or if user clicks on main course window the popup closes automatically.When I use 'goto' with 'open in new window' set as true or 'Display mesage' with 'custom window'- the popup window opens, but user can click on the main course window and even if user closes main course window, the popup window remains open. (Lectora 2008 - course published fo html.Is there any solution to this?