billing.phtml

<form id="billing-form">
    <fieldset>
        <ul>
            <li class="fields">
                <div class="field">
                    <label for="billing:company">Company</label>
                    <div class="inout-box">
                        <input type="text" id="billing:company" class="input-text">
                    </div>
                </div>
            </li>
        </ul>
    </fieldset>
</form>

config.xml

    <config>
        <modules>
            <Namespace_Onepagecheckout>
                <version>1.0.0</version>
            </Namespace_Onepagecheckout>
        </modules>
        <frontend>
            <routers>
                <onepagecheckout>
                    <use>standard</use>
                    <args>
                        <module>Namespace_Onepagecheckout</module>
                        <frontName>onepagecheckout</frontName>
                    </args>
                </onepagecheckout>
            </routers>
            <layout>
                <updates>
                    <onepagecheckout>
                        <file>custom/onepagecheckout/onepagecheckout.xml</file>
                    </onepagecheckout>
                </updates>
            </layout>
        </frontend>
        <global>
            <blocks>
                <onepagecheckout>
                    <class>Namespace_Onepagecheckout_Block</class>
                </onepagecheckout>
            </blocks>
            <helpers>
                <onepagecheckout>
                    <class>Namespace_Onepagecheckout_Helper</class>
                </onepagecheckout>
            </helpers>
    
            <rewrite>
                <onepagecheckout>
                    <from><![CDATA[#^/checkout/onepage/#]]></from>
                    <to>/onepagecheckout/onepage</to>
                </onepagecheckout>
            </rewrite>
        </global>
    </config>

container.phtml

<div clas="container">
    <div id="billing">
        <?php echo $this->getChildHtml('onepagecheckoutbilling') ?>
    </div>
</div>

onepagecheckout.xml

<!-- app/design/frontend/default/mytheme/layout/custom/onepagecheckout/onepagecheckout.xml
-->
<?xml version="1.0"?>
<layout version="0.1.0">
    <checkout_onepage_index>
        <reference name="root">
            <action method="setTemplate"><template>page/1column.phtml</template></action>
        </reference>
        <reference name="content">
            <block type="onepagecheckout/onepagecheckout" name="onepagecheckoutcontainer" template="custom/onepagecheckout/container.phtml">
                <block type="core/template" name="onepagecheckoutbilling" template="custom/onepagecheckout/billing.phtml"></block>
            </block>
        </reference>
    </checkout_onepage_index>
</layout>

OnepageController.php

require_once Mage::getModuleDir('controllers','Mage_Checkout').DS.'OnepageController.php';

class Namespace_Onepagecheckout_OnepageController extends Mage_Checkout_OnepageController
{
    public function indexAction()
    {

        $this->loadLayout();
        if(!Mage::Helper('onepagecheckout')->isOnepageCheckoutEnabled())
        {
            Mage::getSingleton('checkout/session')->addError('Onepage checkout disabled');
            $this->_redirect('checkout/cart');
            return;
        }
        if(Mage::helper('onepagecheckout')->isOnepageCheckoutEnabled())
        {

            $this->getLayout()->getBlock('head')->setTitle('Checkout');
            $this->getLayout()->getBlock('content')->unsetChildren('checkout.onepage');
        }
        $this->renderLayout();
    }
}