Author Template pagination problem….

I am just trying to customize the author template into different section, Example :- we have two columns. In column 1 we want to show posts from cat=1 and in column 2 we want to show posts from cat=3. I have achieved the display for cat=1 and cat=3 but the it shows all the posts from that category . The problem arrives if i limit the posts to certain no. , then the pagination shows links as per the total post count by the author.
Example:- m having 20 posts in cat=1 and 30 in cat=3 and if i limit showposts to 5 for cat=1 it creates pagination link calculating the total posts from the author i.e for 50 posts. The links for cat=1 works and the remaining is left blank.
Hope i have cleared my problem
here is my code…

<?php if (have_posts()) : ?>
<?php
$paged = (get_query_var(‘paged’)) ? get_query_var(‘paged’) : 1;
$my_query = new WP_Query(“cat=5,6&showposts=4&paged=$paged”);
?>
<?php while ($my_query->have_posts()) : $my_query->the_post(); ?>
<div class=”post_excerpt”>

<?php the_excerpt(); ?>

</div>
<?php endwhile; ?>

<?php else: echo “No Post”; ?><?php endif; ?>

<div class=”navigation”>
<div class=”alignleft”><?php next_posts_link(‘« Older Entries’) ?></div>
<div class=”alignright”><?php previous_posts_link(‘Newer Entries »’) ?></div>
</div>