Wireless signal strength is adequate up to about half-way down the building, but in the furthest office it is down to about -88 dB (according to inSSIDer), but amazingly one or two laptops can connect, albeit with agonisingly-slow service.
There would appear to be (at least!) three ways of dealing with the problem.
- get a better router, perhaps with a directional aerial
- put a wireless range extender in the middle office
- put a wireless access point in the furthest office, on the single ethernet cable in that office
(I presume that the wireless range extender would use the same network name/SSID and channel as the main router, and that the WAP should have a different network name/SSID and a different channel.)