As an admin I use a "Send Mass PM" plugin - however I don't want old members who haven't visited the forums logging on to see 100's of old and now non relevant pm's.
Is there a way to remove old pm's sent by a certain user ID?
I think there might be a modification to do that - did you do a search? There is no way to do that in regular vbulletin though. And, if you just do it via clearing out some of the pmtext table, then your pm count will be off for all your users unless you run another query to update that.