x = parseInt(window.screen.width) / 2 - 150;  // the number 300 is the exact half of the width of the pop-up and so should be changed according to the size of the pop-up
y = parseInt(window.screen.height) / 2 - 150;  // the number 300 is the exact half of the height of the pop-up and so should be changed according to the size of the pop-up

function calendar(fieldName)
{	CW=window.open('includes/calendarChooser.asp?fieldName='+fieldName+'','','toolbar=no,menubar=no,location=no,resizable=no,status=no,width=225,height=225,scrollbars=no')
	CW.moveTo(x,y);
}