It'll work with multiple connections from the same IP. It's not recommended of course, and your mileage may vary, but it can be done. All machines with the same IP will login with the same account, just don't select the same character. As long as you select different characters things seem to be ok. If you then do a /who all in the game you will only see the "first" character from that IP that connected. I've got just a couple of folks doing this and it works fine for them to play. To repeat though, this is not recommended since it is possible that something won't work right and it'll hose your database.
bill