Esse aqui aparece centralizado... <html>
<head>
<script LANGUAGE="JavaScript">
<!--
function NewWindow(mypage, myname, w, h, scroll) {
var winl = (screen.width - w) / 2;
var wint = (screen.height - h) / 2;
winprops = 'height='+h+',width='+w+',top='+wint+',left='+winl+',scrollbars='+scroll+',resizable'
win = window.open(mypage, myname, winprops)
if (parseInt(navigator.appVersion) >= 4) { win.window.focus(); }
}
//-->
</script>
</head>
<body>
<!--agradece1.html=pagina da janela - '400','400'=tamanho da janela - no=sem barra de rolagem-->
<a href="agradece1.html" onclick="NewWindow(this.href,'name','400','400','no');return false;">anuncie</a>
</body>
</html>