A base NetBackup server/client install by default will run as a local system account. This will provide enough privileges to perform standard backups and restores. If you are attempting to perform more advanced backups such as Exchange and SQL you will need to modify the NetBackup client service to run as a privileged user depending on what you are looking to accomplish. All of these things are listed in the NetBackup documentation which can be found at:
http://seer.entsupport.symantec.com/docs/290282.htm