combobox and m:n relation

Hi,

i have a project and a task. both have a m:n relation to each other. I made a scaffolding and want to insert a combobox in the task new view

Code : ruby - fold - unfold

    <label for="project_name_ger">Poject</label><br/>         <%= select "task[projects_id]", "project_id",              Project.find(:all).collect {|c| [c.name_ger, c.id]},              :prompt => "Select a Category" %>

the code does not work. does anyone has an idea how to save the combobox's content. it works for a 1:n relation because i just have to save the task which has a projekt_id but with a m:n relations it is different.

thank you