Getting the excerpt to work

Hey guys,

I’m been checking previous posts and experimenting with my own files. I can’t find where I should put this script:
<?php if(is_category() || is_archive()) {
the_excerpt();
} else {
the_content();
} ?>

In my code so I don’t have a big long page full of blog posts to scroll down through.

I tried putting it in the index but nothing happened on the blog page.

Where does this code go?

The index code I’m working with looks like this:

<?php get_header(); ?>

<div class="main">

	<div class="col2">

		<div class="left">

			<div class="content">

	<?php if (have_posts()) : ?>
		<?php while (have_posts()) : the_post(); ?>
			<div class="post" id="post-<?php the_ID(); ?>">

				<h1><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>"><?php the_title(); ?></a></h1>

				<div class="descr"><?php the_time('F jS, Y') ?> by <?php the_author() ?><?php edit_post_link('Edit post',' ~ ',''); ?></div>

				<div class="entry">

					<?php the_content('Read the rest of this entry &raquo;'); ?>

				</div>

				<p class="info">Posted in <?php the_category(', ') ?> having <?php comments_popup_link('no comments &raquo;', '1 comment &raquo;', '% comments &raquo;'); ?></p>

			</div>

			<?php comments_template(); ?>

		<?php endwhile; ?>

			<div class="left"><?php next_posts_link('&laquo; Previous Entries') ?></div>
			<div class="right"><?php previous_posts_link('Next Entries &raquo;') ?></div>
			<div class="clearer"></div>

	<?php else : ?>

			<h2 align="center">Not Found</h2>

			<p align="center">Sorry, but you are looking for something that isn't here.</p>

	<?php endif; ?>

			</div>

		</div>

<?php get_sidebar(); ?>

<?php get_footer(); ?>