That's so awesome! My dream is to fly to Buenos Aires and backpack around Argentina, Uruguay, and Chile. I know those are different places from Mexico, but I'm curious, how were you received as a backpacker? Were people friendly? How much Spanish did you know before going? And did you go with friends?
I knew no Spanish when I arrived (alone, and female and 20), just a couple of words of Italian, so my first day or so was spent saying grazie and prego to bemused locals.
I enrolled in a Spanish language school for two weeks. That gave me the basics, plus I met some people I'd later travel with.
If I wanted to meet more people/ speak English for a while, I'd just head to a beach on the backpacker trail. Despite having always been painfully shy (only child, bookish), I found it really easy to make friends when traveling (and have done ever since, in fact. I guess it served as a lifelong confidence boost). That said, I'd not recommend Mexico now - it is heartbreakingly violent at the moment. I would recommend Argentina and Uruguay! I actually just got back to Europe after a year in Argentina (for work, not backpacking). It's fascinating - the whole sensual-Latin-fiesta thing and, at the same time, a populace that is more self-analytical than Woody Allen and more literary than the NYRB... :)
I wasn't doing much traveling, but the provinces I did visit seemed very safe and friendly to foreigners.