For some odd reason the owner had enabled CLIENT or AP ISOLATION in the router. Be sure to check that since it's now the most common reason that PING would fail.
I just replaced my Syslink router with a new D-Link(model:DGL-4100) router. Before the new router was added I had a home workgroup setup which contained 3 computers (all running XP-Pro). After I installed the new router and built my new workgroup, each computer can access the internet but only one of the computers show up within the workgroup. I can not ping one computer from the other or have any type of file sharing between them. I have repeated the setup procedure from the network wizard in XP many times without success.
Each computer can see the router and use it to access the web but I can not configure them into a working workgroup. All connections are good, and hardware is working. I am not sure where else to look?