Someone from the P2P team internally saw my blog and set me a list of commands to execute and send back to him to help troubleshoot my problem. One of those commands was "net start pnrpsvc". Aha! I hadn't realized that the WinXP Adv. Networking Pack installed any services. Turns out it installs four, including the "Peer Name Resolution Protocol" service (i.e. pnrpsvc). What's odd is that now that I've started it manually once, it seems to autostart on demand now. I can resolve addresses, as well as ping the seed server. GraphChat doesn't work yet, but I think that's because the IPv6 firewall only has two ports open by default - PNRP (UDP 3540) and Grouping (TCP 3587). The GraphChat sample uses a dynamically chosen port, which would be blocked.
So now that I'm back on track, I've got the PNRP namespace provider API wrapped in Managed C++. I can register, unregister, resolve and enumerate PNRP clouds from managed code. I've also got a first pass of the Identity Manager API and a skeleton of the Graphing API done. I'll post code when I have a managed GraphChat sample working.