if (document.images) {
    overviewup       = new Image();
    overviewup.src   = "_images/1-overview.gif" ;
    overviewdown     = new Image() ;
    overviewdown.src = "_images/1-overview_over.gif" ;
    seminarup       = new Image();
    seminarup.src   = "_images/2-seminar.gif" ;
    seminardown     = new Image() ;
    seminardown.src = "_images/2-seminar_over.gif" ;
    speakingup       = new Image();
    speakingup.src   = "_images/3-speaking.gif" ;
    speakingdown     = new Image() ;
    speakingdown.src = "_images/3-speaking_over.gif" ;
    datesup       = new Image();
    datesup.src   = "_images/4-dates_over.gif" ;
    datesdown     = new Image() ;
    datesdown.src = "_images/4-dates_over.gif" ;
    whoup       = new Image();
    whoup.src   = "_images/5-who.gif" ;
    whodown     = new Image() ;
    whodown.src = "_images/5-who_over.gif" ;
    contactup       = new Image();
    contactup.src   = "_images/6-contact.gif" ;
    contactdown     = new Image() ;
    contactdown.src = "_images/6-contact_over.gif" ;
    registerup       = new Image();
    registerup.src   = "_images/7-registration.gif" ;
    registerdown     = new Image() ;
    registerdown.src = "_images/7-registration_over.gif" ;
    sponsorup       = new Image();
    sponsorup.src   = "_images/8-sponsors.gif" ;
    sponsordown     = new Image() ;
    sponsordown.src = "_images/8-sponsors_over.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" );
    }
}