Start by logging into you blog's admin interface at http://blog.gandi.net
Then, on the left-hand side of the screen, in the options menu, click on “Import/Export” which is under the “PLUGINS” section.
This will bring up the list of Import and Export options. What you are doing is exporting a blog, and so you will want to click on “Flat file export”. This will bring up the following interface:
Click on the button that says “Export”.
You will now be prompted to open or save the file it generated. You will want to save this to your computer.
To download your images, click on the link that says “You may also want to download your media directory as a zip file”.
This will ask you if you want to open or save the file called “media.zip”. Choose to save it to your computer.