Creating categories???

Is there a way to let users make a post and create a category for that post?

I was playing with TDO mini forms. But it seems that they can only post to an existing category. I would like it setup so they can write a post and then create a sub category under a predefined category.

For example, If I had a category Birds and I wanted to allow users to post descriptions of specific bird types.
A user could create a post, and create a sub-category called Blue jays.