Sorry if this is a double post but the first time it gave me an error, This should work for you and creates a real Modal now if your looking for one of the fancier modals that are not actually windows use the callbacks like they described.
if (IsDefined(window.showModalDialog)) { retVal= window.showModalDialog(sPage,argsArr, sFeatures); } else { retVal=window.open(sPage,sFeatures+"modal=yes"); } When close the window do window.returnValue=somethign; so you can get the return value. josh