Serial Auto Increment

Let me give a simple example of what I am trying to do:

CREATE SEQUENCE "usernumber" start 0 increment 1;

Create table users (
name varchar(255),
userid int4 DEFAULT nextval ( 'usernumber' ) NOT NULL);
);

>From Borland C++ Builder I create a form with a
link to the table userid and a navigator bar and a DBedit object linked
to the field userid.

When I post new record, an error is returned that users.name cannot be
null, which is true. Is there a way to make Borland C++ Builder only
update the field "name" and let Postgresql take care of the
updating the serial field "userid"

Thanks,
Travis