sale_view.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  sale_quick_payment for OpenERP
  Copyright (C) 2011 Akretion Sébastien BEAU <sebastien.beau@akretion.com>
  The licence is in the file __openerp__.py
-->

<openerp>
    <data>

        <!-- INHERITED VIEW FOR THE OBJECT : sale_order -->

        <record id="sale_order_view_form" model="ir.ui.view">
            <field name="name">sale_quick_payment.sale_order.view_form</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale_payment_method.sale_order_view_form" />
            <field name="arch" type="xml">
                <button name="print_quotation" position="after">
                  <button name="%(open_pay_sale_order)d"
                      string="Register Payments"
                      type="action" states="draft,sent"/>
                </button>
            </field>
        </record>

    </data>
</openerp>