Joomla 1.5 is an excellent CMS for any website, however there are still some modifications that you can make to further optimize your website for search engines. You can improve the joomla core ouput by using tabless html in the joomla core, and also changing out content heading tags to h1, h2, h3 etcc. Joomla 1.5 now allows you to create files in your template folder that will override the Joomla core html output.
A great example for the core html overrides lies within the bees template that comes with every Joomla 1.5 installation. Within the "bees" template there is a folder named "html." You can find the "html" override folder in "templates / bees" directory. This "html" folder contains the core override files. These files override Joomla's core html output, allowing you to modify the html used within your joomla website. With custom core overrides you can change the output of the core joomla code, meaning you can change html tags like div class = "contentheading" and div class = "componentheading" to H1 tags for better SEO. You can also modify any table layouts to div tags allowing for a table-less html output, this can be of great importance when optimizing your website. Since the core html override files are located in your template folder, you can still upgrade your Joomla version while keeping your custom html override files intact.
This is a new feature only available in Joomla 1.5. If you are not familiar enough with html or css to create your own custom html output code, I strongly recommend just copying the "html" folder from inside the bees template, and placing it inside your current template folder. The bees template html override provides a great solution to a table-less core output.