hi
I can't guarantee the author-category combination will work since I haven't tried it, but if it works it will look like this -
query_posts('author=1&cat=-3,-6');
where author=1 is the author id of the author, and cat=-3,-6 means exclude posts that are in those two category ID's. a minus # on categories always means exclude.
I suggest making a custom loop and putting it in the sidebar - this shows up to 5 posts. Note that if a post is in two categories and one is excluded and the other isn't, the post will not be excluded.
<h3>Recent Posts</h3>
<ul>
<?php
$recentPosts = new WP_Query();
$recentPosts->query('author=1&cat=-3,-6&posts_per_page=5');
?>
<?php while ($recentPosts->have_posts()) : $recentPosts->the_post(); ?>
<li><a href="<?php the_permalink() ?>" rel="bookmark"><?php the_title(); ?></a></li>
<?php endwhile; ?>
</ul>