It could be the event 4228 problem or simply that the software is so badly outdated.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.

Aaron,

Thanks again for all of your help.

Please excuse me for being so anal with all my questions but I really want to understand not only what I am doing but why I am doing it. I'm fairly astute with computers but am still green regarding networking.

Before I posted, I checked my event log for error 4228 and found none. I do have static IP addresses set up for my computer to router links.

I have read many posts telling people to port forward but have not done this. My reasoning is that I didn't set up port forwarding from my Win98SE machine and all P2P and torrent programs work just fine. If they work on the Win98SE machine, I'm rationalizing that they should also work on the Win XP machine w/o port forwarding. (after it is finally working, I will update my clients and port forward as you recommend)

Case in point.....
I just installed Opera 9.10 on both machines (without any changes to Opera, or the router. Of course, I granted permission to ZoneAlarm.). Opera 9.10 has an embedded bittorrent client. It will not connect from my Win XP machine but works perfectly from my Win98SE machine. This is the same symptom as BearShare. In my simple mind, this tells me that my P2P and torrent clients and router are OK but WinXP is the problem.

Am I missing something?