UPDATE - BUT STILL NO SOLUTION. I'M NOT ALONE (see above) - IT'S BUFFALO SOFTWARE THAT'S THE PROBLEM. HELP!! please
The XP pc works wirelessly with the "old" (unbranded) router network and ADDON ADDGWU180 802.11g LAN adapter. (It can also "see" the new Buffalo network - just won't get past the "access" log-in, won't accept the password I key in from my manual notes)
The new network set up with the Buffalo router works on my W7 pc with wired access (and wirelessly on my wife's W7 laptop)
SO - I disconnected cable access and tried connecting my W7 pc wirelessly, using the ADDON dongle. W7 "found new hardware", loaded a driver and promptly crashed (BSOD) so clearly the ADDON dongle isn't W7 compatible. Bought a new one (Belkin 150N, both 801.11b and g) - the W7 pc connected to the Buffalo network wirelessly with no problem.
Back to the old XP pc - new dongle, same problem. Can see the network, falls down at "authentication". So - it's not hardware - the problem is I can't get data from the configuartion interface. My pc is totally virus-free, (double checked via external virus check) been defragged. The missing interface data is therefore a BUFFAL software issue not pc related (since contributor "dulybookmarked" has identical the issue - see one-liner above). NOT a good advert for Buffalo gear!
To be crystal clear - typing in 192.168.11.1 (Manual, page 23, "accessing the interface") produces the exact screen shown on page 24 (with data) - but that's all. Pages 32 onwards list the data fields/types which SHOULD appear on the various tabs. BUT - clicking on these tabs results in "transferring data from 192.168.11.1" flashing intermittently (bottom left screen) but no data appearing. AND - as instructed, my firewall is OFF (not a security state I want to continue)..