Previously, I covered the topic of creating custom regions in Drupal 5 themes. However, Drupal 6 introduced a new process for creating custom regions in themes and it is still one of the topics people ask about most frequently.
So, here's a tutorial on how to create custom regions in your Drupal 6 themes. In this example I will use the Garland theme, and insert a new region called 'Uber content', which I'll position above everything in the main content area.

It's basically a two-step process:
UPDATE
The following tutorial covers the creation of custom regions in Drupal 5 themes. If you are using Drupal 6 please see the newer creating custom regions in Drupal 6 themes instead.
----------
All Drupal themes you download will come with a number of pre-defined regions into which you can already place blocks (normally header, left-sidebar, content, right-sidebar, footer), but it can sometimes be useful to create your own.
This can seem a little daunting at first, but it's really just a simple two-step process:
So, lets see how it works.
Step 1 - define the custom region in your template.php file
All themes should have a template.php file contained within the theme folder.
Open the template.php file in your chosen editor and locate the function titled 'function nameoftheme_regions' (where nameoftheme will be the name of the theme to which you are adding a custom region). This will probably be the first function in the file, and should look something like this:
function nameoftheme_regions() {
return array(
'header' => t('header'),
'left' => t('left sidebar'),
'content' => t('content'),
'right' => t('right sidebar'),
'footer' => t('footer')
);
}Okay, now just add your custom region so that it looks like the pre-defined regions.