I have a question about configuring my '/etc/network/interfaces' The setup would be just like this with one caveat.

The “smoothwall machine” would be in a VirtualBox of smooth wall running on a Ubuntu 10.04 LTS 64bit machine with 3 NICS.
Here is my current configuration file for set for DHCP and labels:
## Main intel board
auto eth1
iface eth1 inet dhcp
##Gigabit upper
auto eth0
iface eth0 inet dhcp
##Gigabit lower
auto eth2
iface eth2 inet dhcp
iface lo inet loopback
I really want to try two different scenarios (for learning and in the end experimentation)
Scenario 1. - Virtual Box:
Eth0: will accept wan traffic from my modem,
Eth1: will serve smooth services (most likey with dhcp) to a swtich
Eth2: will be my “fallback” NIC that I will leave alone so I have an easy way to get back online with out too much editing of files.
Scenario 2. is the as Scenario 1 except
Eth0 Via Virtual Box Eth0: will accept traffic from my current router – via dhcp