FYI on this topic of NBU support and RedHat 3 in particular...

Ed, you wrote that:

<snip>
> Fact:  NetBackup 6.5, targeted for release in February, 2007, will drop
> support for RHEL 3.  RHEL 3 started shipping in October, 2003 and will
> be supported by Red Hat through October, 2010.  Symantec will cut you
> off with its current release nearly 4 years before Red Hat stops
> supporting the OS.  On the other hand, Windows 2000, which was released
> 2 1/2 years earlier than RHEL 3, will still be supported by NetBackup
> 6.5.
</snip>

I must respectfully disagree with this "Fact:".

The relevant Symantec publication on this topic seems to be p.3-4 of
the NetBackup 6 OS Supportability Matrix, found here:

http://ftp.support.veritas.com/pub/support/products/NetBackup_Enterprise_Server/278064.pdf

In particular, references to RH 3 include a footnote that reads,

  "Next major release following NetBackup 6.0
   will not support this OS Version.  This status
   could change if market and/or vendor support
   positions change."

For the past 8 years that I've been using NBU and reading these 
supportability statements, the phrase "next major release" has
consistently referred to the next major version number.  
i.e., NetBackup 7.0 (or NBU 8, or NBU 2008, or whatever TPTB 
decide to call it).

So I'm quite confident that these questions don't apply to 6.5.

In my experience, NBU has been good about fully supporting an 
OS revision for AT LEAST as long as the OS vendor is still 
providing general fixes for that version.  For RH3, I think that
will be true until November of this year.  Reference:

http://www.redhat.com/security/updates/errata/

HTH
rob