{HTML options} in collection_select that show pre-selected options?

Seeking rails help....

On a form that is being edited (data is pre-filled), I am trying to
show a collection_select with already selected options that are drawn
can't seem to 'bind' the instance variable to the list:

*** VIEW ***
     <%= collection_select( :tag, :name, @tags, :id, :name,
{}, :selected => @tags_selected, :multiple => true, :size =>5) %>

      @tags_selected = EntryTag.find(:all, :conditions => "entry_id =

My form comes up fine with all of the other data, as well as the items
in the collection_select, but there is nothing pre-selected (there
should be three items selected).

Thanks in advance!