Update: I got it working... This is how I did it in my case. FYI
I posted the following thread:
This is not completely resolved but I got it to work, and the following is how I did it. I'm posting a separate thread to share this with others so those having the same issue might be able to try:
1) Uninstall PowerCMS Builder extension via Adobe Extension Manager. Took it half an hour or more to complete the job. It does act as if it's locked up but I left it running because Activity Monitor showed it was doing something. It eventually finished the job.
2) Reinstall PowerCMS Builder beta build. I used Build 38 which is the latest beta at the time this is posted.
3) Delete .dat file under Configuration folder. The instruction is under "Common Installation Issue" link somewhere in this site.
4) Launch Dreamweaver. Mine is CS4. Set up a DW site and make sure both test server and remote server are set up correctly. In my case, I created a dummy site, set Access to local on both and made sure that the URL Prefix matched the one enabled in MAMP Pro. (That's what I use as a test server.)
5) Try the Quick Start Guide instructions. It worked for me this time, I activated the software with my serial code, and I was in.
6) I ran a setup screen in PowerCMS via browser and it gave me an error saying "PowerCMS" directory and "PowerCMS/Connections" didn't have proper write permission. These directories didn't even exist when I looked inside, so I created both, set both to 777, and just in case I set the site root folder to 777 as well. There was no error after that.
7) After the first time you add PowerCMS contents, the connection name in the PowerCMS Builder dialog would say "PowerCMSConnection". I ignored that, went ahead and added more CMS contents, and they all worked fine.
I still don't know why there was no PowerCMS directory when PowerCMS Builder tried to set up PowerCMS. But the trick I performed seemed to work here. Not sure if it will for other people though.
Come to think of it, I suspect the URL Prefix wasn't correct or not filled out when I first tried. Maybe that was why it didn't do anything...?