I've been teaching myself for the past few years using a similar method to abcdoctor -- flashcards. It is very difficult. I'm American and learned German quickly in school. Chinese? Wow, is it hard. Part of the problem is that there are no multi-syllabic words as in English! Seems most every word is a short sound and when they go by fast spoken by a native Chinese speaker, I have no idea what they're saying. Then when you have to remember the correct tones... whew.