Hi Rich,
An MXP extension can be converted to a ZXP extension using the “Convert MXP Extension To ZXP” tool. This tool can be found in the Tools menu in http://www.adobe.com/exchange/em_download/em6_download.html
For more info, please refer to http://helpx.adobe.com/x-productkb/policy-pricing/dreamweaver-cc-serve r-extensions.html
Regards,
Anit Kumar