best to pm one off the old timers, my guess would be just to make a thread or spend hours pm-ing individually
i presume your meaning like sending 30 at once kind of thing
I don't think phpbb supports this out of the box but I'm fairly sure there is a hack to make it work - vBulletin lets you do this in much the same way as sending an email to multiple people but it costs money.
What I do is have a list of people I need to send things to, for TOTB for example, and then save a shortcut to the link that creates a PM to them: http://www.imoc.co.uk/forums/privmsg.php?mode=post&u=9
Then I open a load of these up and copy and paste my message into each, saves a few clicks but it is a bit of a long way round compared with just adding multiple recipients into one box.
Something that might be possible when the forum moves to the newer version of phpbb perhaps.