Nope - you'll have to install v5.x first.  From the installation guide:

====
You can upgrade to this version of NetBackup only if you have installed
NetBackup 5.0MP4 (or later) or 5.1. If you have an earlier version installed
(for example NetBackup 4.5), you cannot upgrade directly to NetBackup 6.0.
You must first upgrade to NetBackup 5.x and then upgrade. 
====

-M

-----Original Message-----
From: veritas-bu-admin AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-admin AT mailman.eng.auburn DOT edu]On Behalf Of Fernandes,
Eustace
Sent: Friday, December 23, 2005 1:46 PM
To: veritas-bu AT mailman.eng.auburn DOT edu
Subject: [Veritas-bu] Upgrading from 4.5-6


Can I upgrade 4.5MP6 to 5.1 then immediately upgrade to 6. 
1 master also media server 
1 media server, share same volDB, image catalog and robot  
 Eustace Fernandes 
Technical Support 
 <mailto:efernandes AT talisman-energy DOT com> 
voice (403) 237-1534