Sorry for the slow reply: had to wait for the weekend to start mucking about again. Your feedback has been very useful.
KillaB: No chance of that: None of the wires had anywhere near 5V running through them as read on the multimeter. I confess I was getting a quite confused working out the pinouts though.
Kevin: you are right, as noted by bradthebuyer, the cable has PL2303 in it
Bradthebuyer: Your cable differs slightly from mine as mine has a different silver label on it: IL40083821; Nonetheless, like magic, I used your colour combination and I was able to control-c into CFE!
Now I have got into CFE, I cannot actually type anything into it. eg: if I type "help" nothing appears in the hyperterminal/minicom etc. I have tried with and without hardware and software flow control and all sorts of terminal settings. After I have loaded into CFE, should I be able to ping the router across the WAN port? What settings did you guys use for your local IP, subnet, [and gateway]? I have tried static IPs eg 192.168.0.10 and 192.168.1.10
The thing is that I am sure the desktop can communicate with the router as I can get into CFE with control-c. Is this a beginners mistake: have I forgotten to do something obvious?
thanks in advance...