1. Firewalls: disable XP's built-in Internet Connection
Firewall on local area network connections it's for use only on a
direct modem connection to the Internet. Disable and un-install all
other firewalls while troubleshooting.
2. Protocols: Use only one for File and Printer Sharing. If the
network needs more than one protocol, unbind File and Printer Sharing
from all but one of them.
3. NetBIOS over TCP/IP: Make sure that it's enabled on both computers.
Network and Dial-up Connections
Local Area Connection
Internet Protocol (TCP/IP), Properties
Internet Protocol (TCP/IP) Properties
Enable NetBIOS over TCP/IP