Using iptables we were able to access internal machines via their public
IPs using commands similar to:

iptables -t nat -A PREROUTING -i $INTERNAL_INTERFACE -d
$EXTERNAL_ADDRESS -j DNAT --to $INTERNAL_ADDRESS

iptables -t nat -A POSTROUTING -o $INTERNAL_INTERFACE -d
$INTERNAL_ADDRESS -s $DMZ_NETWORK -j SNAT --to $DMZ_GATEWAY

And it worked for years-- no problems.

Now, since I am totally ignorant concerning ipfilter and ipfw, can
anyone unequivocally say that is impossible in m0n0wall?

I'm only curious.

Thanks,

Dave