As David has mentioned the standard client is fine for this, you just need to get a license key to activate the SQL DB agent feature. Make sure when you purchase your license and support certificate you get the right one, they are licensed on the number of physical processors you have in your SQL box:
* Tier 1 is for 1 CPU
* Tier 2 for 2-3
* Tier 3 for 4-7
* Tier 4 for 8 and more
You need to speak to your Netbackup sales person for more info.
One note if you are using Netbackup 5.0, you'll need MP7 to backup SQL 2005 databases directly, NBU 6.0 is fine.