function getViewPort() { 
var vpw; 
var vph; 
var vYscroll; 

if (typeof window.innerWidth != 'undefined'){ 
vpw = window.innerWidth, 
vph = window.innerHeight 
vYscroll = window.pageYOffset; 
} 

else if (typeof document.documentElement != 'undefined' 
&& typeof document.documentElement.clientWidth != 
'undefined' && document.documentElement.clientWidth != 0) { 
vpw = document.documentElement.clientWidth, 
vph = document.documentElement.clientHeight 
vYscroll = document.documentElement.scrollTop; 
} 

else { 
vpw = document.getElementsByTagName('body')[0].clientWidth, 
vph = document.getElementsByTagName('body')[0].clientHeight 
vYscroll = document.body.scrollTop; 
} 

return {w: vpw, h: vph, yScroll: vYscroll}; 
} 

function openOverlayer(id, opts) { 
vp = getViewPort(); 
if (document.getElementById(id)) { 
// alert([vp.w, vp.h, vp.yScroll].join(' ')); 
// alert([opts.w, opts.h].join(' ')); 

overlayer = document.getElementById(id); 

overlayer.style.width = opts.w + 'px'; 
overlayer.style.height = opts.h + 'px'; 
overlayer.style.top = (vp.yScroll + parseInt(vp.h/2, 10+.2) - parseInt(opts.h/2, 10+.2)) + 'px'; 
overlayer.style.left = (parseInt(vp.w/2, 10) - parseInt(opts.w/2, 10)) + 'px'; 
overlayer.style.display = 'block'; 
} 
return false; 
} 

function hideDiv(divName){
document.getElementById(divName).style.display="none";
}