_invoice.html.erb

...
  <td class="Text13Grey numeric">
    <span id="invoice_paid_status_<%= invoice.url_id %>"> <%= partial_payment_in_redbox(invoice) %></span>
  </td>
...

_partial_payment.html.erb

<div id="redbox-for-partial-payment" class="redbox_contents" style="display: none; width: 300px;">
  <div style="padding: 10px">
    <div id="total_payment">
      <table width="100%"  border="0" cellspacing="10" cellpadding="0">
        <colgroup>
          <col width="50%" />
          <col width="50%" />
        </colgroup>
        <tr>
          <td class="CellTablebuttonL">
            <%= button_to_function t('.full_payment'), :class=> "button", :id => "full-payment", :onclick => "fullPayment();"%>
          </td>
          <td>
            <%= button_to_function t('.partial_payment'), :class=> "button", :id => "partial-payment", :onclick => "partialPayment();" %>
          </td>
        </tr>
      </table>
    </div>
    <div id="partial_payment_form"  style="display: none;">
      <div>
        <% remote_form_for invoice_partial_payments_path([invoice, PartialPayment.new]) do |f| %>
          <%= f.text_field :amount, :maxlength => 13, :size => 13, :class => "amount" %>
        <% end %>
      </div>
      <table width="100%"  border="0" cellspacing="10" cellpadding="0">
        <colgroup>
          <col width="50%" />
          <col width="50%" />
        </colgroup>
        <tr>
          <td class="CellTablebuttonL">
            <%= button_to_function t ('.cancel'), "RedBox.close()", :class => 'button' %>
          </td>
          <td class="CellTablebuttonR" align="right">
            <%= submit_tag t('.accept'), :class => 'button' %>
          </td>
      	</tr>
      </table>
    </div>
  </div>
</div>

invoice_helper.rb

...


  def partial_payment_in_redbox (invoice)
    pending = invoice.total-invoice.total_paid
    if pending > 0
      html = render(:partial => 'invoices/redbox/partial_payment', :locals => {:invoice => invoice })
      html << link_to_redbox (format_money_as_decimal (pending), 'redbox-for-partial-payment', :class => "Text13Orange")
      html
    else
      html = format_money_as_decimal (0)
    end
  end

...