WPF - Modal Popup

WPF has a Popup control for this purpose:

http://bhaidar.net/cs/archive/2008/06/29/modalpopup-dialog-in-wpf-browser-applications-xbap.aspx

http://msdn.microsoft.com/en-us/library/system.windows.controls.primitives.popup.aspx

http://roecode.wordpress.com/2008/01/07/wpf-popup-control-part-1-the-quick-and-dirty-way/

http://roecode.wordpress.com/2008/01/08/wpf-popup-control-part-2-user-controls-as-popups/

http://www.highoncoding.com/Articles/470_Introduction_to_WPF_Popup_Control.aspx