Yes, I think this wins the cigar for clever guessing.
1.  I lost access to wireless internet and badly munged
various installations before locating the problem.  (The
wireless modem is on a PC damaged by a power outage,
on which I had to reinstal Win98SE.  That was successfully
done OK but only days later did I notice the OS lacked the
module for /Communications / Direct Cable Connection.
When I installed that, wireless internet and wireless home
network problems just evaporated . . . )
2.  When fiddling in vain as above, this time on the upstairs
(WinXP) station I had the bright idea of trying the ISP's
custom software CD (never needed on the Win98 PC with
the modem, thus never tried.)

I'd bet this is what overwrote in / Tools / Accounts the
server names msnews.microsoft.com (and three others.)
I still owe you the cigar.   Thank you.