Windows media server, right?
I would recomend using the Symantec Tape Device Driver Install wizard (on the NetBackup CD) which can step you through the installation of the latest device drivers. If you do not have a NetBackup CD, you can download the Tape Device Driver Install wizard from the technical support Web site.
To discover devices, NetBackup issues SCSI pass-through commands to the devices in an environment. The server platforms that NetBackup supports may require special operating system configuration changes. Changes may include those needed for device discovery.
For more information, see the appropriate operating system chapter of the NetBackup Device Configuration Guide.