Replacing old server – need advice…

We are putting in a new server this weekend. Two things worry me a bit. Can anybody tell me, or point me to instructions, how to make sure that Exchange and the NT user accounts make the move okay? We are re-installing NT SBS, rather than just doing a backup/restore, because the system was poorly put together originally, and I’m not entirely sure how to make sure that we get Exchange and all the user accounts transferred over. Help? Thanks!