In WordPress 2.9, there will be the ability to add an image to a post, as it's been known of magazine themes. The image need not be insert into the post. With the new feature the_post_image() you can use the new feature and thus control where to display.
The two screenshots show the new post thumbnail dialog when creating a new article. Here you set the picture.
In the template you can use the function the_post_image() to place the image. Here's an example:
<div class="entry"> <?php the_post_image(); ?> <?php the_content('Read the rest of this entry »'); ?> </div>
You can also determine what resolution you want to display.
the_post_image(); // without parameter -> Thumbnail the_post_image('thumbnail'); // Thumbnail the_post_image('medium'); // Medium resolution
Unfortunately, the developers haven't implemented a way to align the image with the classes
alignleft, alignright and aligncenter. And this is how it looks like with the default theme of WordPress: