determining supported timezones

I am trying to figure out if there is a way to determine the timezones
supported in postgresql from within the database. If you look at
http://www.postgresql.org/docs/7.4/static/datetime-keywords.html it
notes that time zone information is system dependent, (I interpret to
mean that anything I find in /usr/share/zoneinfo on linux should be
supported, can someone confirm that?) so how can an external app
determine which timezones are supported given that it could be deployed
against postgresql databases on different OS's.  My current thinking is
that there is no way to get a complete list, but perhaps the list of
known timezones (as listed in the docs) are available?  If it is not,
will this change in 7.5 now that we have a standard timezone library we
are using across platforms?

Robert Treat
--
Build A Brighter Lamp :: Linux Apache {middleware} PostgreSQL