There's quite a few ways:

Self-teaching, colllege/university courses (see if yours offer any), online courses, language exchange/conversation buddy, studying abroad, text books, etc... You can use one method or combination of them all. As far as learning kana (hiragana and katakana) is concern, you can really do it yourself within two weeks. They are dead simple and become almost second nature the more you read.

Just remember that at first you'll be reading at an elementary kid level. I mean, you could read stuff aimed at an older audience but it will take a lot more time, be much more frustrating and in the end might discourage you.

Also some notes on the methods I mentioned:

Self-teaching: there's tons of resources for learning Japanese online if you want a few that I've come across, hit me up and I will share!
Also, check out this thread.

Conversation buddy: what this entails is finding a language partner, someone who knows a language you want to learn (Japanese) and wants to learn a language you know (English). While this might be hard in your area, there's a really cool online resource that uses Skype to overcome this boundary: The Mixxer

Text books: a word of caution, text books can be hit or miss. Each use different methods for teaching. My prof in university would at times correct the text book or say when something was not as common to use. In general they are good, but they are not perfect.

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As for other languages: I am technically bilingual, though my French is a bit rusty. I did the Early Immersion program since Grade 1. Also, my paternal grandmother's family is bilingual (for the most part). Gender in French still smurfs me over every time though.

Oh and took two years of Japanese in university. Not such amazing marks, but was more because I didn't hand in my homework most of the time and didn't study hard enough before my tests. BAD STUDENT IS BAD.