Looking for the most painless way to upgrade our Windows 2000 Active directory domain to Windows 2003 Active Directory.
Note: We do have Exchange 2003 running Active Directory 2000 domain
The most painless way usually is to get a second server, install 2003, join it to the domain, and promote it to a domain controller. You'll need to do a forest/domain prep before joining the 2003 domain controller. Once it is joined transfer FSMO roles, and demote the old server. If the older hardware supports it, you can reinstall 2003 on it, and re-add it to the domain.
Of course before you do anything, your best, first step is to start by verifying you have a good backup.