Exchange Server 2000 backup has skipped files

Does anyone know what files pertaining to Exchange 2000 are naturally skipped by NTBACKUP when a complete backup of all files is done. I have system state and Exchange IS selected. IS is backing up successfully, but when it goes to the directory and tries to backup files individually it encounters them as open and thus reports in the log as skipped. I do a verify and both system state and IS report no errors. When is the MTA backed up in this and when is the .stm files backed up as thses show "in use" and are skipped. Also when are the log files being backed up? Are these part of the IS? I think DS is backed up in the system state since it is AD, isn't it? Thanks for your help. I need to be prepared in the event our Exchange goes south.

En. It seems exchange 2k is too old. Now very popular versions are exchange 2003/20007/2010. I know that ntbackup can backup exchange 2003/2007 under w2k3. So if you want to backup exchange 2003/2007 databases under windows server 2003, ntbackup is a nice choice. Bas thing is that you can't do exchange 2003/2007 under w2k8 since ntbackup is no longer available in w2k8.
If you are familiar with those server OS, you must the Windows Server Backup has replaced ntbackup in w2k8. But Microsoft makes some changes in Windows Server Backup. Thus, it can't backup exchange 2003/2007 anymore. The good sight is that you can use it to backup exchange 2010 under w2k8.
So much I know. Hope what I know can help your guys.