** Can I indeed uplink from a switch to a switch? (The smaller switches have
an uplink port so I don't need a crossover cable.) I seem to think I can,
but someone put some doubt in my mind.

Yes, go from any port on the 24 switch with a straight cable (length up to
100 meters) to the uplink port on the smaller switches.

** Can the DSL router be plugged into the 24-port switch and will all the
clients hanging off the 5-port switches be able to talk through it? Do you
need a straight through or crossover connection for the router > switch
connection?

Yes, just go from the router with a straight cable to any port on the 24
switch - but you need to think about local security because your entire
network may be vulnerable via the DSL connection.

** Will clients connected to the NT and Unix hubs able to communicate with
everything else?

Yes, connect any of the ports on the 24 switch through straight cables
(length up to 100 meters) to the uplink port of the NT and Unix hubs.  If
there is a toggle-switch/button for any uplink port, make sure it is set
properly as uplink.

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