If you have a 6.x client already you just need the update. Check this link: http://seer.entsupport.symantec.com/docs/326385.htm
==========================
III. DOWNLOAD INSTRUCTIONS
==========================
The following procedure explains how to download this Release Update, which
is an update to NetBackup/Media Manager products with the latest fixes for
Windows NetBackup servers.
Download instructions:
1) Download the NB_6.5.4.winnt.x86_<6 digit number>.exe file
into a temporary directory.
where <6 digit number> is an internal tracking identifier
2) Extract the NB_6.5.4.winnt.x86_<6 digit number>.exe
by double-clicking on it.
This will create a number of files that include:
x86.README
and
Setup.exe