also make sure your not overlapping ip adresses
im not a guru so this is just an idea
have your network of computers start with 10.1.x.x, and his 10.2.x.x, bridge them
eg
Code:
1C> <2C
1A>-<2A
1B> <2B
1A = 10.1.0.1, 1B = 10.1.0.2, 2A = 10.2.0.1 etc...
try pinging 2B from 1C etc..