You can self-study from the free sources like,
Tae Kim:
Japanese Grammar Guide | Tae Kim's Guide to Learning Japanese
and,
The Nihongoresources Book:
start [The Nihongoresources Grammar book]
If you use Firefox as your browser you can look into the
Rikaichan plugin for reading kanji that you don't know yet.
You can also take a look at
smart.fm
And you can try to find Japanese sites to read using
www.google.co.jp
This is how I learned Japanese to start with and I did fine with only those resources.
Considering I have never taken a class I think it's easy for me to say that you will jump ahead of your class quite quickly if you put in enough self-study.