I've got NAT up and running reliably (thanks Bob) with a LAN of two 
computers- the NetBSD box (Q700) and my iMac (Rev B).  Twice now I 
have had NetBSD complain:

sn0:  receive buffer area exhausted

after which NAT become erratic at best.  The first time was after 
doing numerous "shutdown now" into single user mode and then "exit" 
back into multiuser mode; I figured that having done this about 30 
times had created the problem and rebooted.  It ran fine for a couple 
of weeks.  Today I rebooted into Mac OS to help my father in law set 
up his ISP account and later in the evening booted back into NetBSD. 
About an hour or so later I got the "sn0:  receive buffer area 
exhausted" message again.  The NetBSD box is currently unplugged from 
the LAN and my DSL connection is direct from the iMac until I get 
this sorted out.

At the same time, my ISP seems to be having some problems; even going 
direct from the iMac I was getting very slow transfers and 
occasionally the link would go down.  The ISP contacted Covad who is 
going to reset the port card on the DSLAM sometime in the next couple 
of hours in hopes this will fix it.  The loop to the CO is clean, 
apparently, so I am wondering if there's some problem external to my 
LAN that is causing the "sn0:  receive buffer area exhausted" problem.

As an aside, my ISP is getting out of the residential DSL gig and 
trying to migrate me to EarthLink.  I'm not going for a variety of 
reasons (especially PPPoE and the lack of a static IP address), but 
this means changing DSL carriers from Covad (no loss) to Qwest. 
Qwest of course ants to sell me their $300 Cisco 675 router; I 
already own a Flowpoint 2200-12 router.  Anyone know if it will work 
with Qwest's Cisco 6100 or 6200 DSLAM?  (Qwest sez "no" but I am not 
sure I believe them).