Assign Name To The DB Users.

I'm developing a vb 2005 application and I€™m creating the users directly to the database. I want to assign them names.
 
I want to do something like this:
CREATE TABLE admin.db_users (
id INT CONSTRAINT db_user_pk PRIMARY KEY,
[name] VARCHAR(50) CONSTRAINT db_user_name_nn NOT NULL,
authentication VARCHAR(25) CONSTRAINT db_user_authentication_nn NOT NULL,
CONSTRAINT db_user_fk FOREIGN KEY(id)
REFERENCES sys.database_principals (principal_id)
ON UPDATE CASCADE
ON DELETE CASCADE
);
GO
 
This is the error that i'm getting:
Msg 1767, Level 16, State 0, Line 1
Foreign key 'db_user_fk' references invalid table 'sys.database_principals'.
Msg 1750, Level 16, State 0, Line 1
Could not create constraint. See previous errors.
 
How do I solve this problem or how can I do something similar.