I'm pretty sure the files on the Kindle with the non .mobi/ non .prc/ non .azw extensions (.mbp? I don't remember) are the ones the Kindle uses to tell what highlights and notes you've made in a book, and what page you were on when you left off reading. The extensions for mobipocket are .mobi and .prc. I have no idea why the mobiguide didn't work the first time, but the extension shouldn't have been a problem; I load .mobi files on my Kindle pretty regularly. I'm glad it's working now, though.
Things I've discovered: 1) not all azw files are DRMed; my Analogs transferred over just fine once I got out the USB cords and moved them from Kindle to Kindle. 2) it's possible to move the .mbp? files from Kindle to Kindle; I did this when I moved my (Gutenberg project) copy of Origin of Species to my new Kindle--I was *not* looking forward to having to re-do my highlights and annotations, since I was 3/4 of the way through and it's a big book.
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Things I've discovered: 1) not all azw files are DRMed; my Analogs transferred over just fine once I got out the USB cords and moved them from Kindle to Kindle.
2) it's possible to move the .mbp? files from Kindle to Kindle; I did this when I moved my (Gutenberg project) copy of Origin of Species to my new Kindle--I was *not* looking forward to having to re-do my highlights and annotations, since I was 3/4 of the way through and it's a big book.