If the diag isn't clear:
1) a PC with 1 NIC and IP address 192.168.0.5 connects via Cross-Over cable to
2) NIC #1 in a PC with 2 NICs. NIC #1 has IP 192.168.0.1 and NIC #2 has IP 10.2.10.5. NIC #2 is connected via Cross-Over to
3) NIC #1 in a PC with 2 NICs. NIC #1 has IP 10.2.10.1 and NIC #2 has IP 65.199.52.10 which is a DSL connection to the INTERNET
PC #2 and PC #3 are both runnint NAT to forward the traffic of the machine connected to their NIC #1