Removing Member Domain Controller / Exchange Server for 2003 Upgrade

OK - SO I have a domain environment that currently consists of four combo AD/Exchange 2000 servers, one of which is sort of an orphan but was kept online as a just in case scenario.  The fourth, orphan is in bad shape, it had a big problem a year ago and needed to have a bunch of files restored from a system hive backup.  It currently hosts an outdated payroll application db that needs to stay online for archival purposes but the fact that it is part of the existing AD / Exchange configuration is going to limit me from upgrading the other domain controller to 2003 architecture and as such I want to start making steps to remove it.  I don't just want to do a demotion without making sure that I have all my ducks in a row with regards to migrating all public folders off, removing it from the exchange groups and assuring that it has no hidden roles.  Can any of your give me pointers on what to do from a methodical standpoint with regards to breaking away the Exchange integration, and then removing the AD on the server.

After I do this initial step, I am going to be going through the steps to upgrade the AD database to be 2003 compatible and then add a couple new 2003 AD\Exchange servers to the existing environments.  Once those are up and running I am going to demote and remove the two oldest servers and then do an inline upgrade of a new server that is running 2000 as well.  Fun days ahead.

Thanks very much for your words of advice.

Ed