I made the proposed changes to the wp-includes/update.php file, and at least got through the initial installation. Thanks.
However, now linking to Site Admin takes me to a directory listing of the wp-admin directory. Clicking the admin.php link delivers a blank page. Any ideas?
EDIT: I forgot to add “index.php” to the Documents tab of the IIS config for this site. Stupid mistake, but I’m leaving this here for posterity.