Thanks Arne

There would be a few hundred providers to start with. The problem I am facing is this:

My office is connected to the outside via a cable line, we have a private static IP. Internally we have a broadband router that also has a built in NAT and Firewall. The client PCs have their own internal IPs like 192.168.x.xxx and the gateway in the settings is the IP of the router.

I start the provider application on my PC and connect to the server and register my IP, but the IP that gets registered at the server is my cable providers gateway IP, not my assigned static IP.

you said---------------
"At the moment I try to build a small private p2p-net using Phex (the forum can also be found in Gnutellaforums).
There you don't have one central tracker, but one host can act as first connection to get you into the network, except, if you'd have a really powerful server and would make the central server the only Ultrapeer.
But here all searches run through the Ultrapeer. "--------

This sounds something that may work for me, could you please elaborate a little more as I am not very clear about this.

Thanks a lot, this is driving me mad!

Cole