Well, the good news is, you've loaded the driver correctly, if you can ping back and forth to at least one workstation.
Why you can only ping the XP box, I'm not sure. What are the relevant IP addresses of the XP, server, and other stuff on the network? Maybe it's a simple subnetting issue?
All of my computers are on 192.168.0.X / 255.255.255.0.
I have fooled around with the networking and it is now mostly working, but i have intermittent drops. From time the VPN or Kerio MailServer Remote Admin just disconnect and take multiple attempts to get a new connection. Very strange.