Network-Attached Servers (NAS) are backed up using Network Data Management Protocol (NDMP)
Since I am not allowed to post URLs, I have attached a file with a Quick Start NAS GUide, an Integration Guide, and a 6.20 support matrix. These documents are all available at the Software Support Organization (SSO) web site
The procedure for backing up a network share can be found in the GUI by clicking Help -> Help Topics, ands searching for NAS