if (document.images) {
    link1off       = new Image();
    link1off.src   = "images/map_map_off.gif" ;
    link1on     = new Image() ;
    link1on.src = "images/map_map_on.gif" ;
    
    link2off       = new Image();
    link2off.src   = "images/map_overview_off.gif" ;
    link2on     = new Image() ;
    link2on.src = "images/map_overview_on.gif" ;
        
}
function linkon( imagename )
{
   if (document.images) {
       document[ imagename ].src = eval( imagename + "on.src" );
    }
}
function linkoff( imagename )
{

    if (document.images) {
      document[ imagename ].src = eval( imagename + "off.src" );
 
    }
}