Pagination is not working properly because of query_post

I am currently using wordpress in creating my websites. And i really find a problem regarding pagination. So basically to be able for you to understand what is really my problem, I will post two codes:

This is the first code:

[ Moderator Note: Please post code or markup snippets between backticks or use the code button. ]

<?php if (have_posts()) : while (have_posts()) : the_post(); ?>

											<div <?php post_class() ?> id="post-<?php the_ID(); ?>">

											<h2><a>"><?php the_title(); ?></a></h2>

											<?php include (TEMPLATEPATH . '/inc/meta.php' ); ?>

											<div class="entry">
											<?php the_excerpt(); ?>
											</div>

											<h3><a>">Read More...</a></h3>
											</div>
<?php endwhile; ?>

											<?php include (TEMPLATEPATH . '/inc/nav.php' ); ?>

											<?php else : ?>

											<h2>Not Found</h2>

											<?php endif; ?>

In this lines of code, I used the regular loop in querying a post. Actually I did not modify the code. I also installed a plugin WP-PageNavi. There is no problem, pagination is working properly.

But when i put this line of code, about the regular loop. Pagination is not working properly. I put this line of code ” <?php query_posts('cat=8'); ?> ” because I want only to show post in this said category.

2nd code:

<---- Line of code ----->
      <?php
											         query_posts('cat=8');

       ?>
	    <---- end line of code ----->

											           <?php if (have_posts()) : while (have_posts()) : the_post(); ?>

											           <div <?php post_class() ?> id="post-<?php the_ID(); ?>">

												<h2><a>"><?php the_title(); ?></a></h2>

												<?php include (TEMPLATEPATH . '/inc/meta.php' ); ?>

												<div class="entry">
												<?php the_excerpt(); ?>
												</div>

												<h3><a>">Read More...</a></h3>

													</div>
										<?php endwhile; ?>

												<?php include (TEMPLATEPATH . '/inc/nav.php' ); ?>

												<?php else : ?>

													<h2>Not Found</h2>

												<?php endif; ?>

My question is: What should i do in order for the pagination to worked properly? I really need some help with this.