Pete's domain registration expired. When that happens, the domain goes into "registrar hold" which means the domain isn't available for sale yet, but it's also removed from all the Name server records, pending payment or deletion.
I suspect that if we'd known the IP of the server, we might have still been able to access the board, depending on how nice phpBB played with IP addesses, instead of the website name.
Oh crap,.. I just geeked out on you guys, didn't I?