Japanese is a very, very complicated language and there's three different writing types for it, as well as honorifics and other tiny add-ons. You're going to have to be seriously dedicated if you want to learn it.
The best way to learn a language is to be surrounded by people who speak your target language. That's what we did as babies, right? Even if we had no idea what the people around us were saying, we adjusted to it. Pimsleur Approach is the best language-learning site that uses that technique, and I would suggest that the most.
Rosetta Stone is okay. It's not well with syntax, and it takes quite a while to learn. It's also really, really expensive. I wouldn't recommend it.
You could even ask some Japanese friends to help you, by talking to you in that language. That will probably be rare and difficult, though.