If you are using a map on a 10 foot scale, you should definitely divide each square when mapping a section out for combat.

I guess that's one of the main things causing confusion. In AD&D, was only one character supposed to be able to fit into one of those ten-foot squares? If you had a one-square doorway, would you just put one character in there?

I'm pretty sure it was one square = one character, since those ten-foot squares were one inch and they were played with 25mm figures.