Problem with the Communication

Hello,

I have 3 PCs in one network. 2 PCs are loaded with Windows XP and the Other with 2003 Server. Each XP PCs are able to communicate between each other. 2003 can able to communicate with each XP PCs. But both XP PCs are not able to establish any communication with 2003 Server.While pinging request time out message is coming.In all PCs Firewall is off and 2003 server is loaded with an antivirus software. Please help me to troubleshoot this issue
Regards
Mohsin