Want to use nicknames for comment authors

I want to use nicknames instead of user names in my comments. This should be simple, right? Sadly, I don’t know PHP, and I’m trying to hack my comment-template.php to accomplish this. After a few hours, I’m at a loss.

Here’s the critical function:

————————–
function get_comment_author() {
global $comment;
if (!empty($comment->user_id)){
$user=get_userdata($comment->user_id);
$author=$user->user_login;
} else {
$author = __(‘Anonymous’);
}
return apply_filters(‘get_comment_author’, $author);
}
———————————-

Basically, I’ve been trying to change user_login to user_nickname and a few other things, but nothing works. I know this part of the code is running, because I can replace that line with $author = __(‘Spiderpig’); and then comments are attributed to Spiderpig, but I don’t know how to access the nickname.

Any help is appreciated.