Windows backup exclude folders? (Ultimate)

I have OneCare which allows me to exclude folders and drives, but
won't save my adminstrator credentials to the NAS share where I want
to put the backups. Scheduled backups fail if the schedule falls when
a non-admin account is logged in. My workaround is to use Windows
Backup and Restore, which properly saves my admin credentials. If the
scheduled backup runs when a non-admin is logged in, it works.

My (perceived) problem now is that the NAS drive to which I back up
has some shares on it mapped as drives on the workstations I'm backing
up. I have all music files stored centrally on the NAS (in
\\nas1\public\music, mapped as M and no music files stored locally.
Local music folders are the standard c:\users\<account>\music.

Because the NAS music share is mapped as a drive letter, Windows shows
it as an NTFS drive. (It's not - it's EXT3.) Windows Backup says that
it backs up only NTFS drives, but there's no way to exclude that
mapped drive.

3 computers all have the same drive mapping scheme to the shared
folder. I'm concerned that backup on each will create multiple
separate backups of the contents of that M: drive. Each computer also
maps U: to the \\nas1\<account> share, and P: to \\nas1\public.

Other than not mapping them, is there any way to prevent Win Backup
from backup up the content of those mapped drives?

Thanks in advance.
--
Chris Cowles
Gainesville, FL