You could always run that as a bat script. Only two command-line commands are needed:
msiexec /i http://status.calibre-ebook.com/dist/win32
or use win64 for the 64-bit version. No need for compiling a program to do the same thing, since msiexec can use an http location. It is (obviously) 64-bit compatible, you can switch it yourself in 8 seconds.
Then if you really need to, you can also add this as a scheduled task, to run every week at 5:00 AM Friday, just hours after it is usually released and in the middle of the night when you're not up anyway.
Based on the discussion here (although it was for linux): http://www.mobileread.com/forums/sho...3&postcount=24
You could always modify that script into a bat script. It was mainly for testing to see if the latest version was installed. The whole discussion was pretty cool though.