Multiport NICs are not expensive, or poorly supported.

Google for Compaq NC3131, they're dual (can be upgraded to quad) Intel
Ether Express Pro 100's on a PCI bridge built into the card. (Note,
these are 64bit/66mhz cards, but they operate fine in 32bit/33mhz slots
unless you opt for the dual gigabit daughterboard)

Other companies have taken various other chipsets and done the same
thing, I recall seeing a quad port rtl8181 based board not so long ago.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5792027257&category=51195&ssPageName=WDVW&rd=1

Quad port tulip chipset based NIC, $4.99 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5791419530&category=51195&ssPageName=WDVW&rd=1

Same card, $19.95 buy-it-now.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5792594592&category=56092&ssPageName=WDVW&rd=1

Lot of 4 Compaq NC3131 (8 ports total) for $40 buy-it-now.

Ignore the clueless people on this list.

On Mon, 2005-07-18 at 14:07 -0500, Randy Clarksean wrote:
> I am looking at a side project (fun/educational) to buy a couple used
> multiport NICs, select a Linux distribution, and make a router/firewall out
> of some old hardware.  Has anyone out there tried this task and had any
> success?  Suggestions on Linux distributions for just a router/firewall
> configuration?  CD bootable versions?
> 
> Quick google search produced:
> 
> Linux router project (now DEAD)
> BBI agent
> Diet-Router
> fli4l
> floppyfw
> FreeciSCO
> Rock Router Linux
> Sisela
> 
> Would be nice if anyone had some thoughts on these or other distributions.
> My goal is to have a secure, solid, remotely administrable system.
> 
> Many thanks in advance ... as always.
> 
> Randy