Are all of your queries to your database "out of the box"? Meaning, are your only database queries those that come built-in to phpBB? Or did you write your own queries for any part of that site or the other sites on that box?
If you wrote your own queries at all, I have some suggestions for diagnosing and optimizing your database. If they're all "out of the box", then there is likely little room for improvement in that area (the queries built-in to phpBB are pretty darn efficient).
Cory von Wallenstein, Dynamic Network Services Inc.
My team and I spent the last few months putting together the DynDNS Spring Server VPS platform for folks needing IPv4 and IPv6 Linux servers on Xen. Would love feedback, both good and bad!