var core=Math.round(4*Math.random()); 

   if (core==0){
document.write('<a href=' + "http://www.es.amnesty.org/" + ' target=' + "_blank" + '><img src=' + "http://www.galeria3d.net/portada/120amnistia.gif" + ' border=0 ></a>');

 }
 
  if (core==1){
document.write('<a href=' + "http://www.msf.es/" +' target=' + "_blank" + '><img src=' + "http://www.galeria3d.net/portada/120msf.gif" + ' border=0 ></a>');

 }
 
 
    if (core==2){
document.write('<a href=' + "http://www.savethechildren.es/" + ' target=' + "_blank" + '><img src=' + "http://www.galeria3d.net/portada/120savechildren.gif" + ' border=0 ></a>');

 }
 
     if (core==3){
document.write('<a href=' + "http://www.greenpeace.org/espana/" + ' target=' + "_blank" + '><img src=' + "http://www.galeria3d.net/portada/120greenpeaced.gif" + ' border=0 ></a>');

 }
 
 
  if (core==4){
document.write('<a href=' + "http://www.fundacionvicenteferrer.org/index.php?cb=QjozLFA6MTg=" + ' target=' + "_blank" + '><img src=' + "http://www.galeria3d.net/portada/120vicenteferrer.gif" + ' border=0 ></a>');

 }