this is what I found on HP's web site:
Tru64 Release Date --------STD Support End Date
V4.0F May 1999 --------Sep 30, 2002
V4.0G Jun 2000 --------Sep 30, 2002
V5.0A Apr 2000 --------Sep 30, 2002
V5.0A Apr 2000 --------Sep 30, 2002
V5.1A Sep 2001 --------Jan 31, 2004
V5.1B Dec 2002 --------Aug 6, 2004
There "WAS" Prior Version Support - Sustaining Engineering (PVS-SE)
But that looks like it ended 2007 as well.
Here is a link:
http://h30097.www3.hp.com/pdf/Tru64U...ge_Current.pdf