Has_many :trough and creating relationships

I got the following application: http://pastie.org/901794 (I pasted
only the most relevant parts.)
It gives an error, while I try to submit the form, specifically:
ActiveRecord::AssociationTypeMismatch in BeiratkozasController#create
Modul(#51370284) expected, got String(#35011620)

It also does this if I change html << radio_button(model_name, method,
option) to html << radio_button(model_name, method, option.id).

It generates the form, and the form works if I comment out the helper,
so it adds the other fields to the database (those fields are not
included in the pastie for length issues), but it fails while I wish
to add the "modul".

Thanks a thousand times and happy Easter!

By the way, does anyone know a more complex tutorial on
has_many :through, since in books I have, and on the net, there are
only basic uses, but I can't find anything that deals with more
complicated situations, like the one in my previous post.

I solved this in a kind of an odd way:

def create
    @student = Student.new(params[:student])
    respond_to do |format|
      if @student.save
        student_id = @student.id
        @subscription = Subscription.new(:modul_id =>
params[:valasztott_training]["moduls"], :student_id => student_id)
        format.html { redirect_to("/hallgato/"+student_id.to_s) }
        format.html { render :action => "new" }

The parameters submitted via a form are always strings (or arrays /
hashes containing strings) - You've ended up supplying a string where
active record expected actual instances of objects.
In this particular case you might try making your form helpers assign
to collection_ids rather than collection