Moving post thumbnails next to excerpts on archives page

I am using Brightpage at http://brianhumek.com. I have a question on the categories/archive results.

For example, at this link http://www.brianhumek.com/category/picture-book-authors/ The image seen there is the featured image in the post it represents. The image is not along side the excerpt, but is above the excerpt title. Is there a way to make this image float alongside the post excerpt?

Also I’d like to know how to do that for the search results too.

I thought the answer would be to edit the archive.php page, but I also found a page called post-excerpt.php in my theme files. I have edited that page which has a some <post thumbnail> code but I do not know how to edit it to make images appear next to the post excerpts.

Any help would be much appreciated.