//img change functions
 function change_on(obj,iscr) {
  document.getElementById(obj).src=iscr;
}	

function change_off(obj,jscr) {
  document.getElementById(obj).src=jscr;
}	
<!--
function emimg()
{
if ((screen.width>=1024) && (screen.height>=768))
{
  document.write('<img src="../Files/empty.gif" alt="" width="800" height="7" />')
}
else
{
if ((screen.width<=800) && (screen.height<=600))
  document.write('<img src="../Files/empty.gif" alt="" width="578" height="7" />')
}
}
//-->