Same presentation for posts archive and posts home page

Hello,

I want to change the theme of my blog, geckoo.org, and I like Atout so much except for the archive pages.
I would like to have the same presentation of the posts archive as the posts in the home page (with thumbnails).

Which file(s) I have to modify ? I don’t know well php and I’m afraid of making some mistakes !

Thank’s a lot for your reply 🙂