var newWindow
function pop(theURL,winName,this_width,this_height) 
{
ax=screen.availWidth; ay=screen.availHeight; 
bx = this_width; by = this_height;
if (!newWindow || newWindow.closed) 
{
features = "location=no,scrollbars=yes,menubar=no,toolbar=no,statusbar=no,resizable=yes,width=" + this_width + ",height=" + this_height;
newWindow = window.open(theURL,winName,features);
newWindow.moveTo((ax/2)-(bx/2),20);
} 
else 
{
newWindow.focus()
newWindow.location = theURL
}
}