>   | and no crashes) to run a dedicated ipfilter/nat machine on a LAN to which
>   | about 1000 PCs are connected.  At maximum, 400 PCs would be accessing the
>   | Internet within a narrow time window.
> 
> What bandwith to the Internet?   If its less than 100Mbps or so, the

Presently there are two connections to the main campus through which we
pass to get to the Internet.  One is an old "telephone" line running at
56Kbps, and the other is a light fiber cable at (I think) 256Mbps.  AFAIK,
the old line is used only for non-proxied http/ftp and to bring in the
mail spool.  The internal LAN is 10base5, but will be upgraded, at least
on some segments, to 100Mbps in September.

Thanks already for the great advice!  The hint about the dual power supply
was invaluable.  I welcome any more comments, again on or off list.  Since
we have no money to hire a professional it makes the operation very difficult.
Your help is appreciated perhaps more than you can imagine.

henry nelson