Movenext in loop without counting

Hi all,
not sure if this is possible or not but here’s what I’m trying to do:
I have:

<?php elseif (in_category(48)) : ?>
<?php if (have_posts()) : while (have_posts()) : the_post(); ?>

…etc, etc

This loops through 10 times and outputs in 2 lines of output with the post excerpt etc.

What i’m trying to do is exclude posts from certain categories within the loop, which is easy enough, but i DON’T want the loop to count. i.e. it outputs 4 then comes across one I want to exclude and it skips over it but will still output a further 6.

at the moment it’s looping through and just showing 9 as i’m skipping one because I don’t want to display, which is half-right.

Hope i’ve explained that ok!