I need to access a Linux box via SSH & Samba that is hidden/connected behind another one.

Setup :-

  
 A        switch    B         C
|----|    |---|    |----|    |----|
|eth0|----|   |----|eth0|    |    |
|----|    |---|    |eth1|----|eth1|
                   |----|    |----|

Eg, SSH/Samba from A to C

How does one go about this?
I was thinking that it cannot be done via IP alone? Or can it?

Could B say "hi on eth0, if your looking for 192.168.0.2, its here on eth1"?
Is this NAT? This is a large private network, so what about if another PC has that IP?!

More likely it would be PAT?
A would say "hi 192.168.109.15:1234"
B would say "hi on eth0, traffic for port 1234 goes on here eth1"
How could that be done?

And would the SSH/Samba demons see the correct packet header info and work??

IP info :-

A - eth0 - 192.168.109.2
B - eth0 - 192.168.109.15
  - eth1 - 192.168.0.1
C - eth1 - 192.168.0.2

A, B & C are RHEL (RedHat) But Windows computers can be connected to the switch. I configured the 192.168.0.* IPs, they are changeable.

Any help?