Hi HeadlessChicken
I've never gotten deep into Mexican cooking, but I certainly enjoy taking a more casual course. I cookbook that I've found very easy to cook from is Rick Bayless
Mexican Everyday. I would say it's a good place to start type book.
Check it out. Oh, don't forget that your local library is a great place to preview cookbooks before you buy them. Even if you don't see a particular book there, still ask! Some libraries have a large pool that they can pull books from.
good luck,
dan