I've never looked at Latin for Dummies. Wheelock is the best text on the subject, but without a teacher you need a companion to it. Wheelock is pretty straightforward, and doesn't do much more than go over the rules, test you on them, and move on to the next subject. Since there are a lot of rules, this makes it a difficult text. The guide I listed puts things in context, and gives a good brushup on how things relate to english syntax, which makes everything go along much friendlier.