> I am looking at the main difference between Veritas Netbackup 
> 5.x and 6.x 
> before doing the upgrade, can someone help with that

  support.veritas.com, which redirects to symantec's PC-oriented site

  Under "support for top products" choose NetBackup Enterprise Server 

  The center of the page is taken up by NetBackup 6.0 Upgrade Portal

  In the "portal," get the upgrade guide, the release impact bulletin
and the release notes.  

_Somewhere_ on the even-worse-than-it-used-to-be-which-was-pretty-bad
site, there might be a Powerpoint with all the new features, like SSO
for NDMP, but that's the sort of thing you should be able to get from
Sales or your vendor.  Perhaps someone on the list has a link to a good
summary of the new features.

But if your question really was "differences," the significant
differences, IMO, are moving the device- and media-related information
from flat-file databases to an included SQL database and rewriting the
scheduling and interprocess communications.  Symantec Training has
two-day v5->v6 difference courses available which cover this and provide
all the block diagrams and changes.

Support was, and AFAIK, still is, recommending opening a case with them
before upgrading so they can help you get your catalog inconsistencies
fixed first, check and validate your upgrade plan, have a case open in
case you have problems, et cetera.