Help using options_for_select in select_tag

<b>Client</b><br />     <%= select_tag 'clients',     options_for_select(     [[' ','1'], ['aaaa','2'], ['daemon','3'],['nortel','4'],['telefonica','5'],['local','6'],['otro','7']] ),     { :multiple => true, :size =>4 }   %>   </p>

Instead of using the ['...', '.'] code I would like to use a method of a list of clients that I have.

options_for_select(@clients.map { |c| [c.name,c.id])