Hello Rechard,
you can know what MAC addresses are behind the 3Com switch.
if f0/5 is the interface that connects to 3Com use:
sh mac-address-table int f0/5
to identify the PCs you should use also the ARP information on the router (that can be the 2960 or another device)
sh ip arp | inc
you can find the ip address associated to that MAC address
Hope to help
Giuseppe