Capability modification for an Author

Hi Folks,
My requirement is simple: I want my WP users publish posts, edit and delete his own posts, but not others’s. Also I want him enable create new categories and edit, delete only his created categories. So I had to make my WP users “Author” by default, not “Editor”. By changing some codes in WP, I can still make “Author” able to create new categories; but the problem is he can also edit, delete all other categories. Is there anyway to do that so that he can create and edit, delete his created categories, but not others’s ?