It could be the event 4228 problem or simply that the software is so badly outdated.
Or both. That would explain the problem with XP. ;]

The same ports would be a problem when the router is online. It can only
forward a particular port to one machine.

The router may also have a firewall of some kind, but it doesn't seem likely
that this is your problem since you didn't change the network card.

Once you do get things working it would be worthwhile to set static internal IP
addresses and set up port forwarding for all the P2P apps. They can get along
with out it but performance and available sources increase greatly once you
get the incoming channels open.