if (document.images) {

   aboutusup       = new Image();
   aboutusup.src   = "graphics/aboutus.gif" ;
   aboutusdown     = new Image() ;
   aboutusdown.src = "graphics/aboutus_on.gif" ;
			
			
			homeup       = new Image();
   homeup.src   = "graphics/home.gif" ;
   homedown     = new Image() ;
   homedown.src = "graphics/home_on.gif" ;
}
function buttondown( buttonname )
{
    if (document.images) {
      document[ buttonname ].src = eval( buttonname + "down.src" );
    }
}
function buttonup ( buttonname )
{
    if (document.images) {
      document[ buttonname ].src = eval( buttonname + "up.src" );
    }
}