Is there a way to make it a requirement to post a thread in the "Introduction" section before the user can post anywhere else?
Not without a plugin no. The only thing you could do is make a group (non-introduced users) and only let them post within the introduction forum. Then you could setup a group promotion to upgrade them to full users once they have a post count of 1.
So, there isn't a plugin available?
Ok, I think I may do that. Thanks for the suggestion