i registered this id just to reply this thread
i am chinese, i got my degree in the states, as you did , and came to japan to work, as a software developer.
even in this field that doesnt ask for too much japanese language skill, still, the very first question of almost all my interview is : can you communicate with your co-workers and independently work on all the documentations?
see... it is really important to know the japanese language, i guess in your case, employers will ask for even more.
i took a minor in japanese in college, however, it didnt work out quite well when i first came here, it really took a while to really communicate...
anyway, i think if you are serious about coming to japan, you need to work on your japanese right away. nothing offensive, most japanese people cannot communicate efficiently in english, you've really got to manage japanese first.