Electro,
Don't let the speaker grill/cover on the door panel fool you. The door speakers are only about 5"(or 5-1/4") in size. The other 2 speakers are:
1. The subwoofer: it's in the passengers side foot well under the carpet, and it's actually not much bigger than the door speakers(it actually might be the same size, I forget).
2. Small 3" rear fill speaker: found between the seats just after the center compartment. You'll see the speaker grill/cover. If you put your ear to it very close, you'll hear a little music coming out of it if the radio/cd/tape is on. I believe this speaker is also used for the OEM phone.
Hope that helps some.
------------------
Richard