You can install PHPBB through Frontpage publishing option however I wouldn't recommend it. You may ofcourse not experience any errors, but I have personally always used an FTP client to install scripts simply because there can be some conflicts with the Frontpage vti-cnf folders that are installed in the folder automatically when you perform tasks inside of Frontpage.
I have experienced a lot of complications with various scripts and I wouldn't always realize that this was the error until I performed a lot of troubleshooting or discovered it in mysql logs. But again you may have no problems with this particular script, so you are welcomed to try it or just use your file manager in cpanel or any ftp client that you can get from versiontracker.com. Hope this helps