if (document.images) {
    aup       = new Image();
    aup.src   = "images/nloff.jpg" ;
    adown     = new Image() ;
    adown.src = "images/nlon.jpg" ;
	
	bup       = new Image();
    bup.src   = "images/deoff.jpg" ;
    bdown     = new Image() ;
    bdown.src = "images/deon.jpg" ;
	
	cup       = new Image();
    cup.src   = "images/enoff.jpg" ;
    cdown     = new Image() ;
    cdown.src = "images/enon.jpg" ;
	
	dup       = new Image();
    dup.src   = "images/froff.jpg" ;
    ddown     = new Image() ;
    ddown.src = "images/fron.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" );
    }
}