Try removing all protocols except TCP/IP. Suggest using dynamic IPs and getting IP addresses automatically from the router DHCP server. It should also provide he DNS info automatically and you should be able to turn-off DNS in the TCP/IP properties.
You may also have to activate the Guest account on XP computers (Start, Control Panel, Category View, Performance and Maintenance, Computer Management, System Tools, Local Users and Groups, Guest, and uncheck Account is disabled, if it is.
When getting an IP from a router DHCP... With the Windows Explorer on the XP computer, right-click My Network Places, Properties, select TCP/IP associated with the network adapter, WINS tab, and select Enable NetBIOS over TCP. The default is:
Use NetBIOS from a DHCP server. If static address is used or the DHCP does not have a NETBIOS setting, enable NetBIOS over TCP.
Share drive: My Computer, right-click C:, Sharing and Security, Sharing. It had drive C: shared as C$, the default share. This share is not visible to other computers on the network. Clicked New Share and added a new share name of C without the . Clicked Permissions and verified that Everyone had full permissions. OK, OK, Apply, OK. Larry