[Nyororin]

Good luck. If you have the determination (and forgiving/neglectful enough parents) it can be done.
One thing I do suggest is making sure you are not around ANY other English speakers... Because no matter how much you may want to learn Japanese, everyone ends up taking the path of least resistance (Ie. talking in English). If you don`t have that option you can`t take it, so you learn MUCH more quickly and efficiently.

I only heard English in the English classes, a couple hours every couple days. Otherwise, it was 100% Japanese. No English speaking friends or anything. It sucked at first - but I was good enough at Japanese to hold an hour long phone conversation after only 3 months. Better than ANY of the English speaking exchange students I encountered were after an entire *year* of being here. They would get stressed and speak to each other in English all the time, so their Japanese never improved much.