Storing information in user registration page in a single table

i want to store the data in the user registration form in a seperate table.Currently my form contains Username, EmailId and some custom fields.Now username and emailId are storing in user table and custom fields are storing in Profile_values table. I want to store Username,EmailId and some of the custom fields in a single table.Is it possible to do it.What is the hook i have to use and how i should proceed