Update - This is being posted from the subject laptop!!! What happened, what was done???
I have absolutely no idea what the magic solution was!!
During the last three days I have consulted, questioned, rehashed, rebooted without count, re-installed windows XP, twice, then XP Pro, once, changed adaptors three times, consulted my ISP twice, reset the router twice, reconfigured the wifi connections at least five times, ... all with the same result - ZILCH, VERY strong signal reception and TOTAL failure to connect. Finally, searching through my collection of "It'll come in handy someday" items, I found a third adaptor BT Voyager 1060 Laptop. Nothing terribly different with this item as compared with the others but nothing to lose, so yet another install. Result? ... This thread input. What happened, what changed? Not a clue - certainly nothing in the reams of troubleshooting advice I've read in the last three days suggested trying another adaptor. Ain't computers absolutely marvellous?
Again thanks to all - unlikely, but this MIGHT just be of help to some other Windows 'victim'