The
first part of learning Japanese is very simple. It's an easy language that isn't tonal, and gender is not indicated grammatically. There are no relative pronouns. Males use different vocabulary than females. Learning without a class will be easy at first, but once you really get into grammar, dialects, and especially Kanji, you will most definitely need a tutor if you actually plan to go anywhere with the language. The language is not directly related to any other language family.
So, to start off, try
Livemocha. It's free, and it's very easy to learn because you interact with others who are learning the same language or your native language. Like everybody else said, though, you will eventually need a tutor if you plan to speak the language properly.