Can't help you with the Blogger backup file question. Your best bet is to copy the generated backup file(s) down somewhere and have a look inside.
Does anyone know a way to export, or export-then-convert, a Blogger blog to a hard drive HTML directory structure that exactly reproduces the blog's online appearance and functionality?
Any "offline browser" site mirroring app can do that. HTTrack Website Copier
is one very good (free under GPL!) example. Info and download links can be found here
HTTrack is a free (GPL, libre/free software) and easy-to-use offline browser utility.
It allows you to download a World Wide Web site from the Internet to a local directory, building recursively all directories, getting HTML, images, and other files from the server to your computer. HTTrack arranges the original site's relative link-structure. Simply open a page of the "mirrored" website in your browser, and you can browse the site from link to link, as if you were viewing it online. HTTrack can also update an existing mirrored site, and resume interrupted downloads. HTTrack is fully configurable, and has an integrated help system.
WinHTTrack is the Windows 2000/XP/Vista/Seven release of HTTrack, and WebHTTrack the Linux/Unix/BSD release.
Note: Do yourself a big
favor and read the instructions first. This app has a slightly odd interface if you're not used to working with this sort of application. It's really important to set the depth
of your mirrored link levels to something reasonable. Otherwise, on a big site, you could wind up attempting to mirror gigabytes worth of stuff you don't really want - and very likely piss off the site's host by generating too much traffic.
I'm a big fan of HTTrack...