To make it a bit more clear: in my form (for edit and new) I have the following:
<% for menu in Menu.find(:all) %> <tr> <td><%= check_box_tag "group[menu_ids]", menu.id, @group.menus.include?(menu) %></td> <td><%= menu.title %></td> </tr> <% end %>
But this is not for what i would like ! (if it is even possible 
)