First you need to install the 6.0 Lotus agent. It's on your "Agents & Options" media. If you don't have that CD, you'll need to download an ISO from FileConnect. You'll need a serial number for THAT. Here's a TechNote:
How to obtain the installation source download and license keys for NetBackup Server, NetBackup Enterprise Server, and components.
http://support.veritas.com/docs/308850
(Let me move back one MORE step - if you need to install the NetBackup 6.0 client, you'll need a different CD/ISO for THAT.)
To bring it up to 6.0 MP6, download and apply the following packs as needed:
Maintenance Pack NB_CLT_60_6_M.tar provides fixes for the Veritas NetBackup (tm) Enterprise Server / Server 6.0 on UNIX clients. NetBackup UNIX Add-on products and Database Agents have separate Maintenance Packs.
http://support.veritas.com/docs/300514
Maintenance Pack NB_ORA_60_6_M.tar provides updates and fixes for Veritas NetBackup (tm) Enterprise Server / Server 6.0 for Oracle Database Agent on UNIX platforms.
http://support.veritas.com/docs/300499
Now, hopefully you have already checked to make sure that the O/S and architecture are supported for Oracle 11g, right? Otherwise, I've had you download and apply a lot of stuff that STILL won't help you. Refer to the table here:
NetBackup (tm) 6.x Database Agent Compatibility (Updated December 8 2009)
http://support.veritas.com/docs/279048
You didn't say WHICH Linux, but there seem to be a few that do have Oracle 11g support starting with 6.0 MP6.
Good luck!