Networking problem

I have 3 PCs attached in a network.1 is running XP and the other 2 2000 professional.All the machines are connected through a workgroup.The 2 2000 machines can exchange the datas ok.But those 2 machines cannot access the XP machine although it is showing in the workgroup list.But the XP machine is accessing the 2 Win 2k machines fine.Even the ping command is showing 'request timed out' from the win2k machines to the XP machine.Is there any chance of incompatability among the OSs?Plz suggest.