Firewall Help

[Justin Wilson]

I am hoping that someone might be able to help me help someone else. 

I am trying to help a friend out who has a small network that he runs
services off of, do to the way he needs his Webservers to access his
Database, he needs a direct connection to the DB server, so he cannot
put his webserver outside his main firewall. So I suggested that he
place his Webserver inside his firewall and run port forwarding to the
webserver, his DNS servers, mail server, and two windows boxes that he
is running VNC on. 

Well the one problem he has is that he has multiple IPs that he is using
for his various servers. All the sample firewall scripts and Howto's
that I can find are for implementing port forwarding are with a single
IP on the firewall and forwarding the various ports on that IP to the
other boxes. So therefore the problem that I have is with the DNS
servers and the VNC systems, they require the same port, so I want to
run multiple IPs on a single NIC on the firewall and forward the ports
from specific IPs to the various boxes that are running the needed
services.

Is this the way to do this or is there a better way, and if it is the
way to do it where can I get an example or a Howto?

-Justin
justin@bigcity.nu