The PM system is set up differently then what we were used to on infopop. It is set up like an email system vs a private thread. Recently I tried to start a group PM for someone who wasn't sure how to do it and I wasn't much more successful. Here's what I eventually figured out.

You can send a PM to multiple users by placing the user names in the receipent field separated by a ; (like with email). However, replies will only go back to the originator of the PM and not everyone it was sent out to.

If you want everyone on the list to be involved in replies, then you should use the "Forward" button instead of the "Reply" button. You would then need to put everyone who is included in the group PM in the receipent field of the Forward.

The catch here is that those receiving the group PM can't see who all the originator sent the PM out to. So if you start a group PM that you want replies to come back to all, then the best bet would be to copy and paste the list of users it's going out to in your first post. That way those responding can do a forward and just copy and paste all those in the group PM in the receipent field.

Hope all the above makes sense.