function mouse_over()
{
  var id;
	id = this.id;
  document.getElementById("menuimg").src = "gfx/layout/menu" + id.substring(id.length-1, id.length) + ".gif";
}

function mouse_out()
{
  document.getElementById("menuimg").src = "gfx/layout/menu.gif"; 
}

for (i=1; i<5; i++)
{
  document.getElementById("menuelement" + i).onmouseover = mouse_over;
  document.getElementById("menuelement" + i).onmouseout = mouse_out;
}