[KidsKilla]

пользуй вот эту ф-цию:

openWin = function(src, w, h, name, prop, txt){
	if (self.screen) {
		sw=screen.width;
		sh=screen.height;
	} else if (self.java) {
		var j=java.awt.Toolkit.getDefaultToolkit();
		var s=j.getScreenSize();
		sw=s.width;
		sh=s.height;
	}
	sw = sw||1024;
	sh = sh||768;
	w = w||sw/2;
	h = h||sh/2;
	var o = {
		resizable:'yes',
		menubar:'no',
		status:'yes',
		scrollbars:'yes',
		address:'no',
		width:w,
		height:h,
		left:((sw-w)/2),
		top:((sh-h)/2)
		};
	if(typeof prop == "object"){
		for(var i in prop) o[i] = prop[i].toString();
		prop = "";
	}
	prop = prop||(function(o){
		var str = "";
		for(var i in o) str+=(i+"="+o[i]+",");
		str= str.substr(0,(str.length-1));
		return str;
	})(o);
	src = src||"about:blank";
	name = name ||"_blank";
	win = window.open(src, name, prop);
	if(txt) win.document.write(txt);
	return win;
};

а вообще всё верно, хоть и неожиданно:
http://msdn2.microsoft.com/en-us/library/ms536652.aspx