Could I share my high speed connection without the cable company knowing about it?

I just got a cable modem and was thinking of
splitting the monthly fee with my two roomates.
The thing is that the cable company charges an
extra 10$/computer for the extra IP adresses. I
was wondering if there is any way of getting
around this. I know that you can somehow arrange
this if you have one main computer that acts like
some sort of doorway to which the other ones are
connected. However, I would like to set it up in
a way that you don't need a computer on all the
time. Is this possible? Could a hub do all this
work? And if so, do you need a special kind of hub?

Thanks!

Hugh