I finished installing a PCI wireless adapter to connect directly to the AP (WHR-G54S) downstairs, (built-in ethernet could not connect via the upstairs WHR-G54S). Finally got my PCI wireless adapter configuration going (58MB download for IE5.5, thanks to lazy programmers) and the Buffalo ClientManager was able to connect to the AP downstairs.
Imagine my surprise - when unplugging the supposedly unneeded CAT5 cable from the motherboard's built-in ethernet, I lost the internet. Plugging it back in brought the web back. Running Winipcfg shows both the integrated ethernet AND the PCI wireless adapter as having connected to the ISP.
In an infinite universe, infinite things may happen.