rescue.rb

  rescue_from ActiveResource::BadRequest, :with => :ar_bad_request
  def ar_bad_request(e)
    @message = e.message
    respond_to do |format|
      format.html { render :template => "#{RAILS_ROOT}/public/something.html", :layout => false, :status => 400}
      format.xml { render :template => "api/something.xml", :status => 400, :content_type => 'application/xml' }
      format.json { render :template => "api/something.json", :status => 400, :content_type => 'application/json' }
    end
  end