While there was no mechanism to "convert" an existing web having a web template to a new web template with FrontPage 2000 or 2002, FrontPage 2003's Dynamic Web Template (DWT) technology DOES allow conversion. 

This design is DWTIG Compliant.  The Dynamic Web Template Interchange Guidelines (DWTIG) have been developed by a consortium of web designers and developers for the purpose of providing guidelines to allow smooth transition when changing from an existing attached DWT design to a different DWT design.

All DWTIG compliant Dynamic Web Templates contain the same editable regions, with the same region names and characteristics, allowing the end user the ability to switch relatively seamlessly from one design to another. Without this compliancy, changing from one DWT to another requires the end user to go through a painstaking process of determining which content in an existing editable region should be placed in which editable region of the new DWT on each and every page of the web.

If this is your initial attachment of a DWT, you must first prepare your existing web.  We have provided step-by-step instructions at http://twcgraphics.com/dwts.