I am while using following to produce a slide for any slideshow from every two posts.

<?php $i = 0; $slideshow_query = new WP_Query("showposts=6&cat=10"); ?>
    <div id="slideshow-posts">
    <div class="newslide">
    <?php while ($slideshow_query->have_posts()) : $slideshow_query->the_post();      $do_not_duplicate = $post->ID; $i++;  ?>
    //my content
    <?php if ($i == 2) { ?></div>  <div class="newslide"><?php $i = 0; } ?>
    <?php endwhile; ?>
</div>

Issue is it produces an empty slide in the finish - wouldso would I recieve it to handle development of a news slide every two posts (or every even publish) except during the last time a level publish happens?

thanks

The operator you are likely searching for is known as modulus or modulo and returns your the rest of a division:

$foo = 5 % 3;           //  5 = 1*3 + a remainder of 2
$bar = 17 % 5;          // 17 = 2*5 + a remainder of 2
$baz = 42 % 6;          // 42 = 7*6 + a remainder of 0

This operator is available in handy to recognize even/odd rows inside a loop when combined with a divisor of two:

0 % 2 => 0
1 % 2 => 1
2 % 2 => 0
3 % 2 => 1
4 % 2 => 0
…

Or perhaps in your situation something similar to this:

<?php $i = 0; $slideshow_query = new WP_Query("showposts=6&cat=10"); ?>
<div id="slideshow-posts">
    <div class="newslide">
        <?php while ($slideshow_query->have_posts()) : $slideshow_query->the_post(); ?>   
            //my content
            <?php if ($i % 2 == 0): /* even: */ ?>
                </div><div class="newslide">
            <?php elseif ($i+1 == $slideshow_query->post_count): /* last: */ ?>
                </div>
            <?php endif; ?>
    <?php $i++; /* iterate in the end */ ?>
<?php endwhile; ?>
</div>

To be able to discover individuals have arrived at the final publish, you can compare $i + 1 (since starting counting from ) using the full quantity of products came back because of your query (max 6 inside your example). After which close the <div> when they match.

UPDATE

I have extended the example above based on my comment. This is not examined, however i believe that's the way i remember results (the publish count that's).