SMBfs mounting OK, listing OK, Read KO, smbclient OK

Realizing that you've moved on to bigger and better things, I still feel compelled to comment....

I've dealt with some pretty crazy setups on much older hardware. Even some with NAS involved, and Samba was the only route to go.

I would recommend looking at the NTFS-style permissions on the files stored in the NAS. If possible, get access to a Windows-based system that can access the share you're mounting, then look at the Permissions of the files. Assuming your smb.conf is using Active Directory (and not "share" or "user" permissions), then any files on the share that permit "Domain Users" to read them, should work.

A very good test would be....can you create a file in the Samba-mount from your RHEL3 system? I realize you're mounting the share read-only, but is it actually shared-out from the NAS with read-write permissions?