NT 4 Domain Migration to AD 2003 user account/passwords

I am planning an inplace upgrade of my NT4 domain this weekend. We have laid out all the plans and I have one remaining question I just cannot find the answer to. In the Microsoft white papers it says that the upgrade will migrate the users and group accounts. I however can find nothing saying if my users passwords will be retained or if they will need to have a new password created. Does anyone know the answer to this question.

thanks