[c-nsp] NAT Question

[Sridhar Ayengar]

I have a NAT question which could probably be considered simple, but my 
Google-fu fails me.  I would appreciate either an answer, or a pointer 
to where I can RTFM.

I have four networks that I'm routing between.  The first is a 
publicly-accessible block for servers with a routeable IP block.  The 
second and third are networks with private IP blocks.  The fourth is, of 
course, the outbound connection to the upstream provider.

Now, as I understand it, the two private networks will be considered 
"inside" for the purposes of NAT, and the connection to the outside 
world will be considered "outside".

What I can't figure out is how to configure the network for the servers. 
  I need the workstations on the private networks to be able to access 
the servers without being NATed, and vice-versa.  Of course, the 
machines on the two private networks need to be able to talk to each 
other as well.

Many thanks for the help.

Peace...  Sridhar

(P.S. I will be adding a VPN in addition to the above, but that's for 
another day, I suppose.)