if (document.images) {
    homebuttonup       = new Image();
    homebuttonup.src   = "images/centrallogo/central_04.jpg" ;
    homebuttondown     = new Image() ;
    homebuttondown.src = "images/centrallogo/central_04_hover.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" );
    }
}