System.xml

<?xml version="1.0"?>
<config>
    <sections>
        <catalog module="catalog">
            <show_in_store>1</show_in_store>
            <groups>
                <stopcheckout>
                    <label>Stop Checkout</label>
                    <sort_order>766</sort_order>
                    <show_in_default>1</show_in_default>
                    <show_in_website>1</show_in_website>
                    <show_in_store>1</show_in_store>
                    <fields>
                        <disable_ext>
                            <label>Disable Extension</label>
                            <frontend_type>select</frontend_type>
                            <source_model>adminhtml/system_config_source_yesno</source_model>
                            <sort_order>10</sort_order>
                            <show_in_default>1</show_in_default>
                            <show_in_website>1</show_in_website>
                            <show_in_store>1</show_in_store>
                        </disable_ext>
                    </fields>
                </stopcheckout>
            </groups>
        </catalog>
    </sections>
</config>