The templates tab is no longer accessible when a file is open in version 1.2. There was a problem with the mechanism in version 1.1 because DesignBuilder users could select model components in a template. When the model was no longer loaded the reference was broken.  To prevent this happening in version 1.2 templates can no longer be modified while a file is open.  You can add, modify and delete your templates and library components from the Opening screen.

Addendum - February 2007

Version 1.3 has this restriction lifted because it includes templates within the model. A beta release with this feature is now available from the Downloads webpages.