Grid layout for posts

On your post div, apply a float:left and define the appropriate width (half of the container’s width since you want two boxes) and height. The float:left will make the boxes move side by side to get the layout you want.

P.S.: Your vertical listing and your grid listing seems contradictory unless your vertical listing has been set to display chronologically, rather than the default reverse chrono order.

I think I got your idea. A sample code would be nice?

Let’s say this is how your posts are formatted in your Main Index Template:
<?php if (have_posts()) : ?>
<?php while (have_posts()) : the_post(); ?>
<div class="post" id="post-<?php the_ID(); ?>">

<h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>"><?php the_title(); ?></a></h2>
</div>
<?php endwhile;else; ?>'

So, each post that comes out will be wrapped by a div of class "post".

Therefore, in your stylesheet, add these to the post div:
.post {
float: left;
width: 200px;
height: 100px;
}’
assuming that your total container (page) width is 400px.

This might or might not be sufficient as it depends from theme to theme.

Thank you. Much appreciated.