One to one mapping does not working in hibernate
===

I am having following tables :

    User                                Profile
    ===========                         ===========
    +userid(PK auto increment)          +userid(PK+FK)
    username                            firstname
    password                            lastname

Now the i have generated mappings with help of Jboss hibernate tool in eclipse
The behavior i want is 
1] User object will be inserted to database (once user sign up i will set necessary fields of this table & send this object to utility class which will save it)
2] Profile object will be inserted to database(now i will set the properties of this table + user object to it & send this to utility class which will save it)

But this behavior i am not getting, please help me how should i do this
i know how the one-to-one mapping works but what should i need to do in order to get this behaviour.

Thanks in advance.