That's strange. If you have a firewall on the 98 machine allow ICMP requests, same with the XP box or you could disable them for testing purposes.

Then try to ping the machines. If you still can't ping verify the IP schema on both machines using the ipconfig command.

e.g. ipconfig /all

Make sure that the IP's fall in the same range and they are on the same subnet.

Also make sure that Netbios over TCP/IP is enabled on both machines.