If a new user has successfully registered in your forum, can an automatic email be sent to them giving them further instructions...
I.e. telling the new user they need to make x amount of posts before they can see the attachments.
I think there's a way to do this but can't find it... ::)
http://support.simplemachines.org/faq/?action=display&faq=93
Just add whatever text you want to the welcome email...