You will need to download NBU 6.5 client software.
Links to all Compatibility Guides:
http://seer.entsupport.symantec.com/docs/303344.htm
NetBackup Enterprise Server / NetBackup Server 7.x Compatibility Lists
NetBackup 7 Operating System (CL) for Client,Server,Dedupe,OpsCenter,NDMP,BMR,SAN Client,MSEO:
http://support.veritas.com/docs/337048
NetBackup Enterprise Server / NetBackup Server 6.x Compatibility Lists
NetBackup 6.x Operating System (CL) for Client,Server,NOM,NDMP,BMR,SAN Client,MSEO:
http://support.veritas.com/docs/325328