Hello Geoffrey,
I just tried the download a few times myself:
http://www.hauptwerk.co.uk/archives/hau ... ptwerk.exe
I had the same problem that you report with one of those attempts when using Internet Explorer, but it has worked fine since. I think it must either by the web server or Internet Explorer misbehaving for some odd reason.
Anyway, just try it again now, if you don't mind. I've tried it about another five times since it gave an error, and it has worked consistently.
Martin.