Domain mapping on pSek.com host

I just installed my first WPMU on pSek.com (their cheapest plan: Personal) and now I want to use the Donncha's Wordpress MU domain mapping plugin. However, I am struggling to make it work.

As far as I can say, I have installed the plugin correctly (including uncommenting the "sunrise" line in wp-config.php). But, I am not quite sure how to do the DNS stuff when mapping individual domains.

What nameservers do I use? Do I need to add the domain to my cpanel? Park it? Any help would be greatly appreciated. Thanks!