Adding Featured Image to Single Post

[apstoller]

Using basic Genesis Child theme -- and need to set up posts so that when you add a featured image, the image shows up on the main archive page as a thumbnail, AND the image will also load larger within the single post page itself (preferably as a medium sized image float right within the post content)

I realize you can simply add your image to the post directly and it will show up as a featured image on the archive page, BUT my client does not want to do that -- they want to add the image to the featured post and have it automatically appear within the content area of the post page.

I couldn't find this in the forum - any help would would be greatly appreciated!