We'll be spending some time in Japan next year so I'm in the process of learning some Japanese too! Here are a couple things I've found helpful:
Like everyone else has said so far, I would learn Hiragana and Katakana first.
I found Drag and Drop Hiragana/Katakana were helpful for practice when I was just starting out. This is really important so that you understand the sounds in Japanese.
http://www.csus.edu/indiv/s/sheaa/pr...ana-timer.html
Of course, if you actually want to be able to read and write Japanese, you need to learn a lot of Kanji as well - blegh!
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Human Japanese, which I got for my phone, is a great introduction to Japanese. Highly recommended. It's much better than a book since you can just click on the screen to hear a native pronunciation.
http://www.humanjapanese.com/home.html
It's only $10 I think and well worth it.
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The best online dictionary:
http://jisho.org/
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lang-8 is absolutely wicked if you're serious about learning Japanese. Basically, the way it works is you correct native Japanese speakers' English, and they correct your Japanese. Even better, most people on there would be happy to Skype with you, so you can actually practice speaking face to face with a native Japanese person. It's a great community and everyone is happy to help out. Of course, you also need to do your part in return but it's easy.
www.lang-8.com