Looks like only ETFs are available, based on the page you linked. The page has the word "institutional" in the web address, and it talks about "qualified investors." Not sure just anyone can use Vanguard from Mexico.
Here's a post from the Boglehead forum on the topic.
http://www.bogleheads.org/forum/viewtopic.php?t=38713It might be worth asking some questions over there, and there must be a Mexican investing forum somewhere online.