First off, make sure your're all on the same switch or the switches used are daisy chained.
Second, just have everyone disable their Windows Firewall unless they know how to set it up correctly and fast.
Third, Make sure there is at most one router/nat on the network as multiple nats could hand out different subnets
Fourth, make sure you're all on the same subnet and can ping each other. I'd go as far as static IPs with the gateway/dns info copied from what you get when you use DHCP.