trouble in passing select tag values in a rails application

new on rails, i am having problem in passing select_tag value(in the
view file) to controller.

my view controller file is like

class ProjectStatusController < ApplicationController

  def index
    @projects = Project.find(:all, :select => "name")

  def show
    lookup = params[:project]
    @rows = Project.find_by_lookup(lookup)
and view file is like

<% form_tag("project_status", :controller => "ProjectStatus", :action
=> "show", :method=>'get' ) do %>
<%= select_tag 'project',
options_from_collection_for_select(@projects,"id", "name"),:onchange
=> "this.form.submit();" %>
<% end %>
if !@rows.nil?
@rows.each do |row|
<%= row[:name] %>
<% end %>

what i basically want to achieve is this - based on the selected value
from select tag i want to display information(on the same view page)
of selected item from the database