var n = Math.random() * 6;
n = Math.floor( n );
if( n < 4 )
{
	document.write('<a href="http://www.nature.org/" target=_blank><img src="/promo/nature' + n + '.jpg" width=120 height=600 border=0></a>' );
}
else
{
	document.write('<a href="http://www.stjude.org/" target=_blank><img src="/promo/stjude.gif" width=160 height=600 border=0></a>');
}