I have a macppc 3.1 machine which I use as an ipnat/ipfilter router
for my LAN.  I installed Samba 3.0.22 from pkgsrc and have configured
it as a public file server (which I will restrict to machines on my
LAN, but have not yet).
I can access shares from a Windows machine on my LAN, using both my
Mac's private and public addresses.
When I use smbclient on the Mac, I can successfully connect to the
localhost and LAN addresses of the server.  When I try to smbclient
with the public address, I get the following after a few minutes:
> $ smbclient //public.addresss.net/public
> timeout connecting to 67.37.*.*:445
> timeout connecting to 67.37.*.*:139
> Error connecting to 67.37.*.* (Operation already in progress)
> Connection to public.address.net failed

Relevant things:
/etc/ipf.conf:
> block in quick on pppoe0 all head 1
> block out quick on pppoe0 all head 2
> ...
> pass in log quick on pppoe0 proto tcp from any to any port = 445 keep state
> pass in log quick on pppoe0 proto tcp from any to any port = 139 keep state
> ...
> pass out quick on pppoe0 proto tcp from any to any flags S keep state keep frags group 2
/usr/pkg/etc/samba/smb.conf:
> [global]
    workgroup = waldo.local