$(document).ready(function(){

  var version = "phpBB3";
 
  var banners = new Array();
 
  banners["1"] = "URL_IMAGEN_BANNER_1";
  banners["2"] = "URL_IMAGEN_BANNER_2"; 
  banners["3"]= "URL_IMAGEN_BANNER_3";
 
  var vsel = new Array();
  vsel["phpbb2"] = "div.nav:eq(0)";
  vsel["phpbb3"] = "p + h1.page-title";
  vsel["punbb"] = ".pun-crumbs:eq(0)";
  vsel["invision"] = "#navstrip"; 
 
  var numforo = $(location).attr('pathname').split("-")[0].replace("/","").replace("f","");

  if(banners[numforo]){
            $(vsel[version.toLowerCase()]).after("<center><img src='"+banners[numforo]+"' /></center>");
  }
});

  var version = "phpBB3";

banners["1"] = "URL_IMAGEN_BANNER_1";

URL_IMAGEN_BANNER_1