It's not precisely freeware, but Windows2000 Backup will handle Exchange 5.5 (and I assume Exchange2000) data. I've done test restores with it with 100% success of priv and pub edb's, no isinteg or any other consistency checking required. With NT4, I was a big Veritas BackupExec (with Exchange Agent) fan, and I believe Microsoft has used a lot of BackupExec in their "native" Windows2000 Backup.
What Win2k Backup won't back up is open user-created data files. It will handle the operating system and the Active Directory, though I have no experience with full restores for either of those.
-Steve