Thanks to all for confirming my suspicions about cable modems and
snooping neighbors.  I noticed in the replies I got that 2 people
recommended getting a cheap x86 (possibly a laptop) and put a couple
if NICs in it to do NAT/Firewall/proxy work.

I have a follow-up for this: Does PC hardware (in general) require
a keyboard and monitor to function?  I remember pulling an 8Mhz
80186 XT clone from the apartment trash one day about 6 years ago,
and seeing the message on the screen "No keyboard found, press F2
to continue."  Despite the obvious lack of design ability by the
people who put a message like that in the BIOS, is that true of
all (or even most) of the cheap older machines I might find?

Remember, the specific desire here is for a machine to fit on the
top shelf of a small linen closet. This will require something
small like a mini-tower or pizza-box sized thing at the largest.
Low power would also be a very good thing, as there will be very
little air circulation in there.

And I would rather not shell out $1000 for this, as it would be a
lot cheaper to make a second network on the unused pairs of the
Cat5 cable running from the closet to the "computer room". Then,
get an SBUS 10baseT (or AUI for that matter) card and use the LX
as a combo NAT/proxy/serial console/X server.  I'd add firewall in
there, but with that many services running, I have a hard time
calling it (or viewing it as) anything like a firewall

To the person who recommended:

     The least expensive and intrusive suggestion I could make is
     to find a $20 Ethernet card and plug it into the pc532, and
     plug that into the cable modem.

Thanks, do you know where I can find such a thing?  I would love
to have a pair of those in my pc532.  <sarcastic flame mode>
[ comments deleted... ] </sarcastic flame mode>

<uninformed and curious mode> The pc532 is not in the x86 ISA family
in any way shape or form, other than the motherboard is "Baby-AT
size" It's processor is the last of the National Semiconductor
32000 line, and it's only expansion is the SCSI bus, the Serial
ports, or the cool hack of pulling one of the serial chips and
putting something else there instead, like a parallel port.
</uninformed and curious mode>

Jon