var win = null; 
function openNewWindow(mypage,myname,w,h,scroll){ 
LeftPosition = (screen.width) ? (screen.width-w)/2 : 0; 
TopPosition = (screen.height) ? (screen.height-h)/2 - 25 : 0; 
settings = 
'height='+h+',width='+w+',top='+TopPosition+',left ='+LeftPosition+',scrollbars='+scroll+',resizable' 
win = window.open(mypage,myname,settings) 
}