Use get_comments()
and pass the post ID as parameter:
$comments = get_comments(
array (
'post_id' => 343
)
);
foreach ( $comments as $comment )
{
// Just to give you an idea of the available data.
// You will probably do something better with it. :)
var_export( $comment );
}
Related: Bug #20572 ($post_id
not passed to comment_open()
from comment_form()
) was fixed just two days ago.