I've created my own magento module and successfully extending core controllers and models but I'm having trouble doing the same with the layout xml files. I want to update just the checkout multishipping shipping page. So far I've only managed to to overwrite the entire checkout.xml file but I would much prefer to just have the in my xml file.
This is what i have in my modules config.xml and the tm.xml file is in app/design/frontend/default/default/layout/
<frontend><layout><updates><checkout><file>tm.xml</file></checkout></updates></layout></frontend>Thanks