if (document.images) {
    btn_about_usup       = new Image();
    btn_about_usup.src   = "images/navi_aboutus.jpg" ;
    btn_about_usdown     = new Image() ;
    btn_about_usdown.src = "images/navi_aboutus_over.jpg" ;
	
    btn_contactup       = new Image();
    btn_contactup.src   = "images/navi_contactus.jpg" ;
    btn_contactdown     = new Image() ;
    btn_contactdown.src = "images/navi_contactus_over.jpg" ;			
				
   btn_manufactureup       = new Image();
   btn_manufactureup.src   = "images/navi_mlinks.jpg" ;
   btn_manufacturedown     = new Image() ;
   btn_manufacturedown.src = "images/navi_mlinks_over.jpg" ;
							
btn_homeup       = new Image();
btn_homeup.src   = "images/navi_home.jpg" ;
btn_homedown     = new Image() ;
btn_homedown.src = "images/navi_home_over.jpg" ;
}
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" );
    }
}