I found (what appears to be) a very useful page:
http://www.15seconds.com/issue/040708.htm
It has walked me through setting up <div id="service" style="BEHAVIOR:
url(webservice.htc)" onresult="DisplayResults()"></div> and
useService / callService commands. I think it's almost there, except
that the actual call returns "fault string = service unavailable".
Now trying to figure out why the service is unavailable...
(heavy sigh)
Dan