I'd say that the HowToJoomla Site's article pretty much sums up the process.
Here is the process with a few more steps added - hopefully this will help.
I am assuming you have got as far as packaging your extension and have been able to get your css and javascript files to install on the server. They may be in your module folder, or probably more correctly they should be within your modules sub-folder under the /media/ folder.
If after installing the module you can not locate your css and js files it is because you haven't referenced them correctly within your component's xml installation file. This page contains info about the xml installation / manifest file for 1.6/1.7 add-ons although it is for a component: http://docs.joomla.org/Developing_a_Model-View-Controller_%28MVC%29_Component_for_Joomla!1.6_-_Part_01 they are very similar.
Either way - find your files within Joomla's folder structure and make a note of their relative path from the root of the website - ie the folder containing configuration.php
Now somewhere within your module's php - add the line that gets a reference to the JDocument object.
$document = JFactory::getDocument();
Now add the line that adds your javascript to the html head area:
$document->addScript('url/to/my/script.js');
obviously replace 'url/to/my/script.js' with the actual relative path to your javascript.
Now add the line that adds your css to the html head:
$document->addStyleSheet('url/to/my/stylesheet.css');
again adjust the path - it may for example be media/mod_mymodule/mymodule.css (if your module were called 'mymodule').
Only things to be aware of are that you need to add these lineswithin executable php tags NOT within a html area after exiting php mode.