window.onload=function(){
 var viewportheight;
 
 // mozilla/netscape/opera/IE7
 
 if (typeof window.innerHeight != 'undefined')
 {
        viewportheight = window.innerHeight
 }
 
// IE6 

 else if (typeof document.documentElement != 'undefined'   && typeof document.documentElement.clientHeight != 'undefined' && document.documentElement.clientHeight != 0)
 {
          viewportheight = document.documentElement.clientHeight
 }
 
 // older IE
 
 else
 {
          viewportheight = document.getElementsByTagName('body')[0].clientHeight
 }


document.getElementById('maintable').setAttribute('height',viewportheight);
}