I have 2 PC's on my network. They are in the same Workgroup and same gateway and same subnet mask, same DNS and both were connected to a managed switch. One is windows 2000 the other is windows XP. Trendmicro & Windows XP firewalls have been turned off. Independantly of one another they can both access all servers and the internet. Each of these PC's can also ping a 3rd PC but they cannot ping each other. We tried a separate test by disconnecting them from the network and we set them up side by side with a cross over cable connecting them. Nothing changed.