var nDialogWidth=750;
var nDialogHeight=720;
var nLeft=(window.screen.availWidth-nDialogWidth)/2;
var nTop=(window.screen.availHeight-nDialogHeight)/2;
var sFeatures='dialogLeft:'+nLeft+'px;dialogTop:'+nTop+'px;dialogHeight:'+nDialogHeight+'px;dialogWidth:'+nDialogWidth+'px;help:no;status:no';
var bLogged=window.showModalDialog(A.aspx,window,sFeatures);