We would like our users to post a small introduction about them selves as their initial post, is there any way we can enforce this?
There is no fully automatic way to do this. Maybe this discussion can give you some ideas?
You could try something like making all categories read only to level 0 (or 1?)and set getting to the next level dependent on getting a certain number of likes.
Then they could post in that category and be stuck in level 0/1 until their intro post had received likes.
Other solutions with custom badges exist.