function getWindowHeight(win) {   
     if (win == undefined) win = window;   
     if (win.innerHeight) {   
         return win.innerHeight;   
     }   
     else {   
         if (win.document.documentElement   
             && win.document.documentElement.clientHeight) {   
             return win.document.documentElement.clientHeight;   
         }   
         return win.document.body.offsetHeight;   
     }   
 }
        

window.onload = function ()
{ var h = getWindowHeight()-120 + 'px';
document.getElementById('inhalt').style.height = h;
}