def index
  	if params[:query]
    	@posts = Post.search(params[:query])
    else
    	@posts = Post.find(:all)
    end
    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @posts }
    end
  end


<% form_tag posts_path, :method => :get do %>
  <p>
    <%= text_field_tag "query", "size" => 30 %>
  </p>
  <p>
    <%= submit_tag "Search" %>
  </p>
<% end %>