puzzled network scheme

[hydros]

Hello All.

 Could anyone recommend me a solution of the following network
 problem:

           Here is a planned network map
 
             - Internet ISP -
                    |
                    |
                    |
                    | real ip address 213.x.x.x
                +-------------+
                |FreeBSD 5.3  |
                |  Box        |
 Interface 1    +-------------+ Interface 2 (ethernet 100mbit)
 real ip address|             | real ip address 194.x.x.x
 194.x.x.x      |             |
 (ethernet      |             |
  100mbit)      |             |
                              |
                      +Simple Ethernet switch +----------------A few boxes with a real ip
                              |                                  addresses 194.x.x.x
                              |
                              |
                              |
                              |
                              |
                              |
                              |
                              |
                              +-----A few boxes with a private
                                    ip addresses 192.168.x.x

 The general question is  how to combine the real IP addresses
 and the private on the same physical interface.
  I`m planning to use natd for my private addresses on the Interface 2 because the traffic
 billing (http://netams.com).
 I`d be very thankful for any help.

--
Best regards,
 hydros                          mailto:hydros at mail.ru