Nyororin and jasonbvr have lots of very useful information posted..
to join in, I also live and work in Japan. I've been here for 2 years already. Although the only information I know about the English-teaching community is from a friend of mine. I tried applying at schools, just for the sake of it, and they say that I am not a native english speaker so they did not accept me heheh, well there goes my attempt of being a teacher.
How to learn Japanese in a fast way? Join lots and lots of classes , japanese classes. Actually its cheaper learning Japanese here than at home because there are lots of volunteers willing to help you. Go to your local city hall and ask for a list of Japanese volunteer class. And interact with lots of Japanese and don't be shy speaking to them and ask them if they could correct your grammar, don't get irritated or angry if corrected but instead be greatly, you find that Japanese people are really helpful if you show them that you are interested and very much willing to learn.
In learning the language you have to have an idea which part of the language is your priority. In my case, I can't concetrate in all aspect like reading, writing and speaking as I have struggle also with work so the time being I concentrate in conversation/speaking and a bit of reading, and if I can familiarization in Kanji. It also help that I was sent to a client with no foreigner and no one can speak English. So my week was like work till friday , in all Japanese and then classes on Saturdays , Sunday was my only rest day where I talk with my friends.