var popupWin;
function openWindow(url,name) {
var winwidth = 640; // width of the new window 
var winheight = 480; // height of the new window 
var winleft   = 200; // just dummie values
var wintop    = 200; // just dummie values

if(parseInt(navigator.appVersion)>=4)
{winleft = (screen.width / 2) - (winwidth / 2); // center the window right to left 
wintop = (screen.height / 2) - (winheight / 2); // center the window top to bottom 
// the values get inserted into the features parameter of the window.open command... 
}
popupWin = window.open(url
    ,name 
    ,'menubar=no,toolbar=no,location=no,directories=no,status=no,scrollbars=no,resizable=yes,top=' + wintop + ',left=' + winleft + ',height=' + winheight + ',width=' + winwidth);
if (window.focus) {popupWin.focus()}
}