Most modal scripts rely on checking the browser every second to make sure the window is on top. Not a particularly friendly thing to do. You could write a script so that onBlur the window is refocused, but there are ways around that too.
The IE modal property, in addition to being IE only, has problems passing data back to the originating window.
The best method is to either use a hidden div that becomes visible or to use an AJAX call. [ March 01, 2006: Message edited by: Marc Luzietti ]