No, you can have a Firewall, even so the wormhole is still there but it is blocked...
There is a big problem with XP - Service Pack 2, I may be not too accurate, but Microsoft blocked and limited the Internet traffic on a XP SP2 to just 8 connections simmultaneusly, this is a living death for most people using P2P programs (ex: the infamous and worthless Kazaa)...not to talk about people who use it's machine as a server, I think there was an unlicenced or unufficial patch going around in order to break this limitation...(Microsoft say: "We did it again", we f****d a lot of users)