a page where posts display inline, 3 in a row?

Yes, using CSS

make the width of the post area one-third or less the width of the container the posts are displayed within, and set the post divs to float left.

It will take a little bit of additonal tweaking but that’s the main change that’s required

Yea do something like

<div id="container">
<?php if(have_posts()): while(have_posts()) : the_post(); ?>

  <div class="post" id="post-<?php the_ID(); ?>">
    <h3><?php the_title(); ?></h3>
    <p><?php the_content(); ?></p>
  </div>

<?php endwhile; else: ?>

  <div class="post">
    <h3>Error!></h3>
    <p>There is no content because you didn't make any posts yet!</p>
  </div>

<?php endif; ?>
</div>

Then style it.

#container {width:900px; margin:auto; height:auto; }
.post {width 300px; height:100px; float:left;}

Something like that, i really didn’t take much time so there might be a few errors,