Prova con questo.
ciao Enzo


on (release) {
nameWin = "gatto";
uUrl = "gatto.html";
wdth = "375";
hdth = "491";
scrollbars = "no";
toolbar = "no";
menubar = "no";
resizable = "no";
status = "no";
location = "no";
left = "((screen.availWidth/2)-(" add wdth/2 add "))";
top = "((screen.availHeight/2)-(" add hdth/2 add "))";
getURL("javascript:window.open('" add uUrl add "','" add nameWin add "','height =" add hdth add ",width=" add wdth add ",top='+" add top add "+',left='+" add left add "+',toolbar=" add toolbar add ",scrollbars=" add scrollbars add ",resizable=" add resizable add ",status=" add status add ",menubar=" add menubar add ",location=" add location add "'); void(0);");
}