What kind of service does the NAS drive offer? Samba, NFS?
First in the firewall, open up the tcp/udp ports used for browsing. You will probably have better luck that way.
Enter "smbclient -L <ip address of NAS>". Are the services listed?
For NFS, you can use the showmount command to show the services offered.
Try to connect in konqueror by entering
in the address bar.