Hidden field for admins only?

Hi, I am hoping someone can help get me pointed in the right direction.

I am looking for a way to add a field to a post’s edit page. This field would only be available to the Admin usergroup; regular Authors would not see it. Also, the text entered into the “hidden” field wouldn’t actually publish out to the site…it would just get written to the DB, and stay on the post’s “edit” page. Kind of like a “notes” section for a given post.

Is there a plugin to do this, or any other possibility?

Thanks
Malcolm