This is a great idea.

I think the best way to go by this is to simply 'close' off the thread creating features and thread commenting features in all other topics apart from Introductions. Then after their first post, the Beginners pick-up topic can be opened up to them. Then after 5/10 posts all other forum topics can be opened up to them.

Sure fire way to filter out the spammers and keep the genuine members.