OT...great books

[Randallw]

narf poit chez BOOM said:
That's because the Belisarius series is written by Eric Flint, despite David Drake's name on the cover,

I've always wondered about stuff like that. When there are two authors, who writes what?. I've got a Turtledove book cowritten by Richard Dreyfuss. Do they write half of it each, did Dreyfuss come up with the idea and let Turtledove actually write it, or do they spend hours on the phone (or in a forum) comparing notes.