Export your Blogger blog thanks to the premium feature. Then, download this script and run it like that :
php transform_overblog.php export.xml http://my-blog.com lucile@evhell.fr ldaguise Ldaguise non-classe
export.xml
: the xml file to transformhttp://my-blog.com
: the blog URLlucile@evhell.fr
: the Wordpress superadmin mailldaguise
: the Wordpress superadmin loginLdaguise
: the Wordpress superadmin display namenon-classe
: the category name where Wordpress put posts without categories
This script doesn't dowload files to the media library. You can use Import External Image plugin to do it after importing the transformed XML file. I also used Auto Post Thumbnail to assign a thumbnail to each post.