hmmm,
If it's anything like my office's setup (ADSL) I'd have thought your computer network workstations should generally be on the LAN side of the router, adding more switches on the LAN side to expand as necesary, with the modem, on the WAN side of the router.
You'd allocate a fixed IP from the external address to the router, and can then have your internal 192.168 range for the workstations. If you need to the router should be able to have a separate PC (s) in a DMZ, or issued with fixed external IPs.
With your setup, I can't see how the router would allow stuff that is on it's WAN side to see stuff that is on it's LAN side especially if they both are in the same IP range
