Add paragraph tags to comments

You should structure your comment so it would use the “comment_text” build in function or even easier should use a fallback function that would structure your comment…

For example in twenty ten it looks like this:

function twentyten_comment( $comment, $args, $depth ) {
$GLOBALS['comment'] = $comment;
switch ( $comment->comment_type ) :
    case '' :
?>
<li <?php comment_class(); ?> id="li-comment-<?php comment_ID(); ?>">
    <div id="comment-<?php comment_ID(); ?>">
    <div class="comment-author vcard">
        <?php echo get_avatar( $comment, 40 ); ?>
        <?php printf( __( '%s <span class="says">says:</span>', 'twentyten' ), sprintf( '<cite class="fn">%s</cite>', get_comment_author_link() ) ); ?>
    </div><!-- .comment-author .vcard -->
    <?php if ( $comment->comment_approved == '0' ) : ?>
        <em><?php _e( 'Your comment is awaiting moderation.', 'twentyten' ); ?></em>
        <br />
    <?php endif; ?>

    <div class="comment-meta commentmetadata"><a href="https://wordpress.stackexchange.com/questions/48348/<?php echo esc_url( get_comment_link( $comment->comment_ID ) ); ?>">
        <?php
            /* translators: 1: date, 2: time */
            printf( __( '%1$s at %2$s', 'twentyten' ), get_comment_date(),  get_comment_time() ); ?></a><?php edit_comment_link( __( '(Edit)', 'twentyten' ), ' ' );
        ?>
    </div><!-- .comment-meta .commentmetadata -->

    <div class="comment-body"><?php comment_text(); ?></div>

    <div class="reply">
        <?php comment_reply_link( array_merge( $args, array( 'depth' => $depth, 'max_depth' => $args['max_depth'] ) ) ); ?>
    </div><!-- .reply -->
</div><!-- #comment-##  -->

<?php
        break;
    case 'pingback'  :
    case 'trackback' :
?>
<li class="post pingback">
    <p><?php _e( 'Pingback:', 'twentyten' ); ?> <?php comment_author_link(); ?><?php edit_comment_link( __('(Edit)', 'twentyten'), ' ' ); ?></p>
<?php
        break;
endswitch;
}
endif;

so… you can include this code or embed it in your functions.php then make
it a callback default like so.. :

wp_list_comments( array( 'callback' => 'twentyten_comment' ) );

.
The difference is this part:

comment_text()

.
You can read here about: comment_text()

.
Hope this helps 😉
Best of luck, Sagive.