/**
 * source: http://www.quirksmode.org/viewport/compatibility.html
 * get available inner height
 */
function availHeight()
{
  var x,y;
  if (self.innerHeight) { // all except Explorer
    x = self.innerWidth;
    y = self.innerHeight;
  } else if (document.documentElement && document.documentElement.clientHeight) {	// Explorer 6 Strict Mode
    x = document.documentElement.clientWidth;
    y = document.documentElement.clientHeight;
  } else if (document.body) { // other Explorers
    x = document.body.clientWidth;
    y = document.body.clientHeight;
  }
  
  return [x,y];
}