hatch back means it has a hatch meaning it opens from the back end as well. my friend has the exact same car, and unless yours has been welded shut its a three door (hatch is considered a door in most cases). When your sitting in the drvier side, reach down with your left hand and there should be two levers. one for the trunk release and one for the gas tank flap.
If its an STD then it has the black center peice to the taillights and has no insignia (no DX, no Si).
and what are saying about this "1-2 behind the seats"? You have all sorts of room for a sound system, and itll sound great cause of the acoustics of a hatch.
heres a good forum for hatchies:
http://www.civichatchback.com/board/index.htm
and thisll give you anything else you want to know:
http://www.civic4g.com/