I have fixed the problem, in case it's worth anything to anyone else. Or at least I have removed the problem and can download again.
In Add/Remove Programs, when Internet Explorer is selected, an option exists to return to your previous browser. I tried that, and lo and behold IE6 was uninstalled, I was returned to IE5 as my browser and I can now download again, even if it sent my address book into the ether. (Why do I suspect it wouldn't work if your previous browser was Netscape?)
This was obviously a new feature on IE6 as the same option doesn't appear in IE5, but who cares? I can download again, whooo hooo!!!