you have to have diferent "set" of ipnumbers on each network. as i have no idea what order you have things conected i just give a possible case.
eth0 is 192.168.0.X
eth1 is192.168.1.X
notice the diference that the second "series" (the number/s separated with dots) from right is a 1 not a 0.
eth2 213.XXX.YYY.ZZ this is because your internet provider likely uses an completly difetrent range of ipadresses.
this way your computer can easily tell them apart.
it "may" be possible to use same but it wil make the network DEAD slow, like a few bytes second MAX, that is 1-2b/s instead of 10 000 000b/s, actually it should be only the errors coming trough...