Go to Catalog–>Manage Categories. When adding a new category, you have options in the “dispaly settings” tab to show products or static block only. Then you select the static block (you’ll have to have created one yourself) and make sure that in “Custom Design” you select the appropriate template and layout. And don’t forget that in the “general information” tab to include in the navigation menu.
Hope that helps! Magento is sure far from Joomla or wordPress in terms of content management, and load time is not the greatest, so you might also consider using the Blog extension from http://www.aheadworks.com or the WordPress plugin here on HT to display static content. Then you can add links to the nav menu in your template phtml files.