Linking tables?

If I had a table containing a list of usernames and another few tables where each line in the table included one of the names and some other information (1 to 1 relationship).

How do I set up the mySQL tables to insert a new row into each of the other tables (containing the default data) when a new name is added to the initial table?

ie.
tblName (USERNAME, firstName, surName)
tblSecurity (USERNAME, password)
tblSex (USERNAME, sex)

>> I want it so when you insert a new entry in tblName it inserts (automatically) an entry in tblSecurity containing the username and default password and an entry in tblSex containing the username and default sex.

I find it safest to do three seperate inserts, using the same username in each insert for example

insert tbl_1 (field1,field2) values ('bob','somedata')

(execute the query)

insert into tbl_2 (field1,field2) values
('bob','somedata')

(execute the second query)

insert into tbl_3 (field1,field2) values
('bob','somedata')

(execute the third query)

hope that helps!!!