function new_window(url) {
if (document.all) 
{var xMax = screen.width, yMax = screen.height} 
else if (document.layers) {
var xMax = window.outerWidth, yMax = window.outerHeight
} else {
var xMax = 640, yMax=480
}; 

var xOffset = (xMax - 560)/2, yOffset = (yMax - 250)/2;

window.open(url,'Email','toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=0,width=535,height=250,screenX='+xOffset+',screenY='+yOffset+',top='+yOffset+',left='+xOffset+'');
}