I have a excellent understanding of *nix systems, however networking is where I am almost clueless. Does anyone have any suggestions on accomplishing the following?

Computer B
Should not have networking beyond Computer A
Running service on port X
Connected to switch

Computer C
Should not have networking beyond Computer A
Running service on port Y
Connected to switch

Computer A
Two NICs (One connected to WAN, one connected to switch)
Should be able to access Computer B service by calling localhost:X and Computer C service by calling localhost:Y.

iptables seems to be the way to go in regards to forwarding the ports (NAT), but how would I go by setting up the dual NICs in this configuration?

Thanks

there's nothing at all interesting about the dual nics here. it's just two different networks, there's no complex config whatsoever.

What do you mean by "calling localhost:X"? obviously A has to connect to B or C directly at some level as there's nothing else there to facilitate it. what protocols are we talking about? What is the use case for this environment? Why can B or C not reach past A?

I'm assuming that host A is front-ending hosts B/C and hence the services X/Y on hosts B/C are accessed via host A.
Setup the 2x NICs on two separate IP subnets, enable static NAT rules on host A to forward service X coming into host A from WAN side to service X on host B, etc.
You need to do a little reading on howto Static NAT using iptables.