MR is about the best technical help you can get, seeing as the fellow who posted 2 posts up from me (Kovid) happens to be the guy who (primarily) wrote calibre.
Try getting
that kind of people to talk to you from BigHugeSoftwareCo.
As for your download problem, I'd advise downloading,
then running -- there are fewer opportunities for Windows to throw fits that way. Also, the advice to download from Sourceforge is good. Like any program, calibre is at the mercy of its download sites, and it seems that the primary one has issues.