Try changing the network settings on each machine to manually set an IP address (Turn off DHCP) - you may need to set up another profile or switch this back on to get the PC's to play nicley on other networks you use.
Then set one to say, 192.168.1.10 and the other to 192.168.1.11
If it asks about subnet's accept the default 255.255.255.0
Reboot and it should work.
Best rgeards
Memetic.