you can still using standards template (index.php) and follow these steps :
1. search for this line <? query_posts(); ?> in the index of your template
2. replace with <? query_posts('showposts=1'); ?>
3. finish
if you'd like to using homepage.php instead index.php, copy code below t your homepage.php
<? query_posts('showposts=1'); ?>
<?php if (have_posts()) : ?>
<?php while (have_posts()) : the_post(); ?>
<div class="post" id="post-<?php the_ID(); ?>">
<h2>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></h2>
<small><?php the_time('F jS, Y') ?> <!-- by <?php the_author() ?> --></small>
<div class="entry">
<?php the_content('Read the rest of this entry »'); ?>
</div>
<p class="postmetadata"><?php the_tags('Tags: ', ', ', '
'); ?> Posted in <?php the_category(', ') ?> | <?php edit_post_link('Edit', '', ' | '); ?> <?php comments_popup_link('No Comments »', '1 Comment »', '% Comments »'); ?></p>
</div>
<?php endwhile; endif ?>