Getting the number of posts in a category

Ok, I’ve found a couple different resources that deal with this issue but not quite in the way that I need it. I’m not very fluent in PHP so I’m having a hard time nailing down the syntax and whatnot.

Here’s what I’m trying to do: I want to take my category “Videos”, get the number of posts in the category an then chop it into 3 numbers so I can display all of the posts in 3 close-to-equal columns.

Here’s the code I have, I’m fairly certain it’s close just not quite working, so if I could get some help I would really appreciate it. Thanks in advance.

<?php
/*
Template Name: Vids
*/
?>
<?php get_header(); ?>
<?php
$vidsTotal=(get_categories('15')->count); <strong>This is the problem I think</strong>
$vidsFirst=floor($vidsTotal/3);
$vidsSecond=floor(($vidsTotal-$vidsFirst)/2);
$vidsThird=ceil($vidsTotal-($vidsFirst+$vidsSecond));
?>
<div id="VidsLeft" style="width: 600px; margin: 2px 2px 2px 0;float:left;">
                <div id="LeftLeft" style="float:left;width:300px">
		<?php query_posts('showposts=$vidsFirst&offset=0&cat=15'); ?>
		<?php while (have_posts()) : the_post(); ?>
			<div class="text" align="center">
			<h3><a href="<?php the_permalink() ?>" rel="bookmark" title="Continue reading <?php the_title(); ?>"><?php the_title(); ?></a></h3>
                        <br />
			<?php
			$values = get_post_custom_values("vid");
			if($values != "")
			{
			echo "<object width='200'><param name='movie' value='$values[0]'></param><param name='allowFullScreen' value='true'></param><param name='allowscriptaccess' value='always'></param><embed src='$values[0]' type='application/x-shockwave-flash' allowscriptaccess='always' allowfullscreen='true' width='200'></embed></object>"; }
			?>
                        <?php $values = get_post_custom_values("vidAlt"); echo $values[0]; ?>
                        <br />
                        <?php the_excerpt(); ?>
                        <?php endwhile; ?>
                        </div>
                <div id="LeftRight" style="float:Right;width:300px">
		<?php query_posts('showposts=$vidsSecond&offset=$VidsFirst&cat=15'); ?>
		<?php while (have_posts()) : the_post(); ?>
			<div class="text" align="center">
			<h3><a href="<?php the_permalink() ?>" rel="bookmark" title="Continue reading <?php the_title(); ?>"><?php the_title(); ?></a></h3>
                        <br />
			<?php
			$values = get_post_custom_values("vid");
			if($values != "")
			{
			echo "<object width='200'><param name='movie' value='$values[0]'></param><param name='allowFullScreen' value='true'></param><param name='allowscriptaccess' value='always'></param><embed src='$values[0]' type='application/x-shockwave-flash' allowscriptaccess='always' allowfullscreen='true' width='200'></embed></object>"; }
			?>
                        <?php $values = get_post_custom_values("vidAlt"); echo $values[0]; ?>
                        <br />
                        <?php the_excerpt(); ?>
                        <?php endwhile; ?>
                        </div>
</div>
                <div id="RightVids" style="float:Right;width:300px">
		<?php query_posts('showposts=$vidsThird&offset=($VidsFirst+$VidsSecond)&cat=15'); ?>
		<?php while (have_posts()) : the_post(); ?>
			<div class="text" align="center">
			<h3><a href="<?php the_permalink() ?>" rel="bookmark" title="Continue reading <?php the_title(); ?>"><?php the_title(); ?></a></h3>
                        <br />
			<?php
			$values = get_post_custom_values("vid");
			if($values != "")
			{
			echo "<object width='200'><param name='movie' value='$values[0]'></param><param name='allowFullScreen' value='true'></param><param name='allowscriptaccess' value='always'></param><embed src='$values[0]' type='application/x-shockwave-flash' allowscriptaccess='always' allowfullscreen='true' width='200'></embed></object>"; }
			?>
                        <?php $values = get_post_custom_values("vidAlt"); echo $values[0]; ?>
                        <br />
                        <?php the_excerpt(); ?>
                        <?php endwhile; ?>
                        </div>
<?php get_footer(); ?>