>>Problem is, how do I set up the many to0 many relationships? <<
You set-up a many-to-many relationship between tables by creating what is sometimes called a "resolver" table (goes by other names as well). In your case, you will have tblURL and tblCategory; in which 1 URL can have many categories and each category can have many URLs. Your tblCategoryURL merely contains 2 fields, the primary key field from each of the other tables. So, the resolver table is then the "many" side of 2 one-to-many relationships, one with each of the other tables.