Hmmmmm... kind of a tough question to answer.
You do not need an XML editor. You can just copy out the parts of the sip.cfg and phone1.cfg file you want and paste them into the my-site.cfg and my-phone.cfg files. The only thing you need to watch with XML is that the information is in the same case and uses the same ending structures as the generic files.
You dont need to have a separate my-site.cfg or my-phone.cfg file, you can use the main ones. Modify sip.cfg for your site, and then just copy phone1.cfg to my-phone.cfg and make changes. Then in the MAC-Address.cfg you only tell it to load my-phone.cfg and sip.cfg as part of the CONFIG_FILES line.
An XML editor might make life easier if you aren't familiar with XML, but most XML editor's i've ran into are for web pages, and trying to open the XML file with excel will cause it to crash (too much info in there).
I would HIGHLY HIGHLY suggest you go to voip-info.org and search for "Polycom Provisioning". It is a required read, available here:
VoIP-Info.org Polycom Section I would also highly recommend you read the Administrator's Guide to Sip 2.2 from polycom. It's available here:
Polycom IP320/330 Support Page
