A common end user question surrounds the use of Microsoft or third party templates for SharePoint. For non server side templates (ones that you can upload yourself to the Site template gallery on your SharePoint) you can simply go to the Site Setting area of the site and click on Site Templates > Upload. Pretty easy. But here's the catch: what if you want to use this template to create your top level site? Since the Site Actions menu is not exposed during template selection it is not immediately obvious how you would do this. Here's the trick. You need to add \_layouts\settings.aspx to the URL of your site and then simply navigate to the Site templates gallery of the site and upload your template. After this, just return to the URL of the top level site and refresh the page by clicking F5 on your keyboard. Now you will see your template in the list of options available to you. Pretty neat.
Here's a tutorial on how to perform this task, "Adding a .stp SharePoint site template prior to the selection of the top level site template through the SharePoint web UI" Click the screen grab below to watch. (PS you need SilverLight).