Yes, it is very simple. Just duplicate the single.php and rename it to something else. For example, single1.php, then remove <?php comments_template(); ?> from it.
Use this code:
<?php
$post = $wp_query->post;
if (in_category('1')) {
include(TEMPLATEPATH.'/single1.php');
} elseif (in_category('2')) {
include(TEMPLATEPATH.'/single2.php');
} else {
include(TEMPLATEPATH.'/single.php');
}
?>
[Please post code snippets between backticks or use the code button.]
Make sure you replace the category number above.