the 404 error you are getting when adding CMS Builder has to do with the site settings. It is most likely an issue with the URL Prefix (Web URL in DW CS 5.x)setting for the testing server. make sure the URL PRefix for the testing server is configured to a proper address for your site.
it sounds like you copied an older version of the cms files from the other site.
you can get the CMS files in the Dreamweaver Configuration folder. to locate the configuration folder, see the Common Installation issues PDF;
common_installation_issues.pdf
in the configuration folder go to shared/webassist/PowerCMS/CMS for the power cms files.
I would delete the existing CMS files and use the ones from the configuration folder instead.