habtm relation, cannot populate join table

Hai friends, I hav two models related with habtm

class User < ActiveRecord::Base   has_and_belongs_to_many :station,                           :join_table => "stations_users",                           :foreign_key => "user_id",                           :association_foreign_key => "station_id"

class Station < ActiveRecord::Base   has_and_belongs_to_many :user end

When i create a new user its user_id and the station _id is not inserted into the "stations_users" table.I hav used scaffolding 4 creating these two models.How can i insert the fields for the join table also when a user is created? Can any one help me?

Thanks and regards, Veena