>>"we used to notify users that a planned shutdown was over"

I think what he wants to do is send a message to PC's that are not logged
on in an active session because the machine was shutdown for maintenance,
backups, patches, etc.

Probably the easiest way to make this work is to shift our thinking process
and just simply use JTMAIL, SENDMAIL, etc to e-mail the users when the
machine is back up and running.  If you use the correct phrasing in the
subject line, the users e-mail reader could make noice that an urgent
message has arrived.. and to logon.

JTMAIL, SENDMAIL, and other packages are available on the HP e3000. It
should be an easy task to set up.  You would need to maintain a routing
list of who to contact.  And that is where the new LDAP client for the HP
e3000 comes into play...