if (document.images) {

aboutup       = new Image();
aboutup.src   = "images/button-about-0.png" ;
aboutdown     = new Image() ;
aboutdown.src = "images/button-about-1.png" ;
kontaktup       = new Image();
kontaktup.src   = "images/button-kontakt-0.png" ;
kontaktdown     = new Image() ;
kontaktdown.src = "images/button-kontakt-1.png" ;
agbup       = new Image();
agbup.src   = "images/button-agb-0.png" ;
agbdown     = new Image() ;
agbdown.src = "images/button-agb-1.png" ;
startseiteup       = new Image();
startseiteup.src   = "images/button-startseite-0.png" ;
startseitedown     = new Image() ;
startseitedown.src = "images/button-startseite-1.png" ;
}
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" );
    }
}