if (document.images) {
    botomapup       = new Image();
    botomapup.src   = "css/empresa/botomap.gif" ;
    botomapdown     = new Image() ;
    botomapdown.src = "css/empresa/botomap2.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" );
    }
}