> IV  Get new machine to do NAT use the SMC EZ Card 10/100 that the cable
>     installer left behind because I did almost all his work for him.

This would be my recommendation....only put two NICs in the machine.  One
internal, one external.

> Also, does the cable modem broadcast all my 10baseT traffic to the
> neighborhood, or just the traffic between my single provided IPv4
> address and their router?  If the former, I think I'd like a full
> firewall to hide the local traffic...  (I guess a switched Ethernet
> hub could do the job, but I suspect my 5 port $20 hub isn't up to
> that task.) I could spend a few hundred on this, but I'd rather
> keep the costs as low as possible right now.

Most cable modem systems are shared media.  Think of it as one big piece
of 10Base-2 coax.  Some cable providers program their modems to filter out
simple stuff, like NetBIOS over IP...mainly to keep all the windows users
from sniffing each other's shares.  But you can sit on your local cable
modem and watch traffic from everyone else.