Theming the forum topic list to have picture of last posted user

hi,
I am using the Drupal forums module to enable forums in my website.

I want to theme the forum's topic list (list of threads) page using the recommended forum-topic-list.tpl.php
I have two questions:

1. Do I need to change the "./modules/forum/forum-topic-list.tpl.php" file itself, or can I copy this file somewhere in my theme directory and customize it. I really dont want to change the core file, but I am not able to figure out how to get it to pick the file from my theme directory. Like the zen theme can I create a "
/templates/forum-topic-list.tpl.php" and it will work ?

2. How do I get it to show the picture of the user who last commented on the topic ? I'm just not able to figure out how to do this. Does anyone have an example of a forum-topic-list.tpl.php to show how its done?
Do I need to use template_preprocess_forum_topic_list for it ?

any help would be much appreciated.