Hmm...
Well, I've been following h.p with interest.
Until a few moments ago, I still had not been able to download an x64 2.1 installer, though I have not tried the proxy trick. Certainly I started out using IDM, but gave up on that, and used Firefox, took forever, and produced the same result.
Got a bit excited when h.p reported success using Chrome - big let down.
Eventually I decided to use IE11, went to download.com, and told it to use the secure route. Couldn't believe it when the 64-bit Revision Number checked out (Thanks, @BetterRed, for that). Held my breath, and ran the installer. Allowed Calibre to start, and it identified itself as calibre 2.1 [64-bit]! Yay!!!
Thanks to all who have contributed to this thread. Without the discussion, I'd not have realised I was somehow repeatedly ending up with the 2.0 installer package.
I still do not know how this happened, and whether, when the time comes, I shall be able to download 2.2 without problems. I have always use Internet Download Manager for my downloads, and have never had a problem with it, but once I got past
The specified account already exists, which only happend a few times right at the start, I started to detect warning messages from IDM telling me the download was corrupt.
It really was the discussion which prompted me to try the download.com secure route, being aware that they keep their own copy of Calibre, so thanks again for your help.
Now, I dare say, I shall just have to wait and see.