Replace:
Code:
getURL("http://www.promo842.com/Advent/day" + url_id + ".htm", "_self")
with:
Code:
getURL ("javascript:NewWindow=window.open('http://www.promo842.com/Advent/day" + url_id + ".htm','newWin','width=450,height=300,left=0,top=0,toolbar=No,location=No,scrollbars=No,status=No,resizable=No,fullscreen=No');  NewWindow.focus();void(0);");