Taz,
Few things to check.
1 - Firewall rules, check you don't have a firewall that is blocking each machine from seeing each other(disable firewall for testing)
2 - Check that all your machines are looking at the same network, If you are not using a router that assigns an IP address (or if you are just using a bog standard switch) then give you machines an IP address (plenty of guides on the net to do this)
I always advise to have all your machines built the same way, same firewall/virus scanners etc, and always ensure your machines are patched upto date, with licensed software.