Hey folks! Thanks for all of your supportive messages. I got it installed with no problems, but ran into a few issues when doing the PHPBB import. I've solved it and was able to import everything successfully - now it's configuration time!
(For those who are interested): The PHPBB database was old... MySQL4 and was on a different server than the new XenForo database. I wound up importing the old database into an empty MySQL5 database on the same server as my new XenForo one, and then the import went smoothly. Also, the file paths to avatars and files required the complete path.
Thanks again to everyone for answering my presale questions. I look forward to getting to know you folks!
Congratulations and welcome aboard! Don't forget to associate your forum user name with your license here: http://xenforo.com/customers/forum-users to post in the support forums, and have access to resources.