Alright, I've gotten a little further. I tried uploading a backup from one single author, which was a much smaller file. (I didn't think this was an issue though, since I maximized the upload limit from 2MB to 20MB via .htaccess)
It gave me this message:
Unable to create directory /public_html/wp-content/uploads/2008/09. Is its parent directory writable by the server?
Keep in mind, all permissions are 755. So I checked via FTP and no such folder was even created. I tried creating the folders, and now it's telling me:
The uploaded file could not be moved to /public_html/wp-content/uploads/2008/09.