var textnumber = 2;
var randomnumber = Math.random() ;
var rand1 = Math.round( (textnumber-1) * randomnumber) + 1 ;
text = new Array

text[1] = '<a href="http://www.leemails.com/index.php?p=registro&r=121264" target="_blank"><img src="http://www.leemails.com/inc/img/banners/120x600.jpg" border="0" alt="Leemails.com"></a>'
text[2] = '<a href="http://www.es-facil.com/ganar/alta?Id=65347467&dd=60001020304"><img src="http://banners.es-facil.com/muestra_banner.php?d=6534746760001020304" border=0></a>'

var mytext = text[rand1]
document.write(text[rand1]);