How to call query_posts from functions.php?

Hi,

I need to create a function in functions.php that goes through all the posts in a specific category (to display their titles and some related pictures).

I have created the first version of the function like this:

function showPosts($category_name)
{
query_posts(‘category_name=$category_name&showposts=10’);

while (have_posts()) : the_post();
$title = get_the_title();
endwhile;
}

Problem is that nothing is displayed. It looks like the query_posts call fails, but why is that? And what can I do about it?

Thanks,
Mads