Adding foreign key to User model

I'm sure there is an easy way to do this, but I can't seem to make it work. I need to add a couple foreign key references to the User model (defined in the admin application). I've imported the admin User, but it still fails to resolve it. Does it need to refered to it by it's full class name?

Custom linking of models in many-to-one relationship

I have a model that can be attached to a variety of different models, based on the value of a column. Is there any way to map this relationship in Django? If not, is there a way to automatically do post-fetch processing where I could populate it? Here is a example: class Note(models.Model):