Need Help, file sharing through the netw

I have 3 winXP prfessional version + 1 winXP home version workstations working behind the D-Link 4port router switch,which connects to internet.The thing is I cannot make the files in the different workstations be shared,each one can see the shared folders,but cannot access them. I opened the firewall on each of the workstation,but no access either. Another scenario is I cannot ping each other workstation’s IP, although if ping its self is OK, and when I checked the file’s property,there is no tab named permission, I don’t know why. I am stuck there.