Milo, I don't know!! It's just I that I would like to transfer files between my Mac and the HP via ethernet.
You can do that without IPv6, just using IPv4. Don't add the IPv6 to your life if you don't have to... its only going to come back and bite you in the backside when you're trying to troubleshoot some unrelated problem down the line.
Look in System Preferences and Sharing on the Mac.... you'll find a number of options in there that you could use to get your PC to connect to your Mac (e.g. FTP, SMB).
Alternativley, if you want to spend a bit of cash (and assuming its compatible with the version of OS X and non-intel processor running on your G5), take a look at Thursby DAVE. Install that on your Mac and you can connect to Windows shares as if you were a PC. Time-limited demo version available I believe.