The "cheapest" way do do that is to dig up an
old hub (or inexpensive switch) and "uplink" out of
the current switch to the "even older" hub.
(Sounds like you have already gotten them a new
router though, so this may be N/A or a moot point...)

I do that all the time for Internet facing computers.
Then when I want the Internet "OFF", it hit my uplink
button (on the older hub) , and that blocks the hub from
passing anything on to its own (3) connections.
(The Router/switch still works normally for my wife, etc.)

This turns  4 router & 4 hub connections into 3 & 3 connections.
(Works best with limited traffic, like in a home network.)

                                         Rick Glazier

From: "Will Stephenson"
>I have a client whose network is beginning to grow beyond the 4 port router
> that had previously served them well. I'd like to attach the old 4 port
> router to the new 8 port router and have it act like a switch/hub. Is this
> possible? If so, what changes do I need to make to the old router to make
> that happen? (I did disable the old router's DHCP)

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