You'd need to use an advanced HTML theme for this sort of thing. The code to put in your theme's qa-theme.php file would be something like this:
class qa_html_theme extends qa_html_theme_base
{
function vote_count($post)
{
if ($post['netvotes_raw']==0)
$this->output('MY SPECIAL THING FOR ZERO VOTES');
else
qa_html_theme_base::vote_count($post);
}
function a_count($post)
{
if (isset($post['answers']) && ($post['answers']['data']==0))
$this->output('MY SPECIAL THING FOR ZERO ANSWERS');
else
qa_html_theme_base::a_count($post);
}
}
More information about advanced themes here:
http://www.question2answer.org/advanced.php#theme-advanced