application_helper.rb

  def form_file_field(form, attr, options = {})
    options[:class] ||= ""
    options[:class] += " span12" unless options[:class].include?("span")
    content_tag :div, :class => "input-append", "rel" => "pretty-file" do
      form.file_field(attr, :class => "hide") +
      text_field(:file, attr, :class => "disabled #{options[:class]}") +
        link_to(t("browse"), "#", :class => "btn")
    end
  end