OK, decided to try another computer, someone else's laptop...with a recent install of 8.1 Pro 64-bit. Went to the download page for GE, and got this:
"Garmin Express is not compatible with your operating system. You will need to upgrade your OS to use Garmin Express."
Is this a joke?!
http://imageshack.com/a/img661/1011/dstsZj.jpg
To the page's credit, it does say this down the page:
"Garmin Express is not compatible with your operating system. You must upgrade your OS to use Garmin Express, or you can use legacy software called Map Updater to update maps on automotive devices."
Tried the page with both Firefox (37.0.2) and IE (11.0.9600.17728), and got the same unbelievable message.