How to make window unaccessible?

["Evgeny Repekto" <repekto argosoft gmail com>]

Hi,

In my GUI application user is able to open small window under the main
window to put into some data. I would like to forbid for user to work
with main window until he closes small window  as like it is done with
dialogs. Window that is openeing the dialog is unaccessible.

Please, advise me how to implement this feature.

Eugene.