Assumming that your file is read through STDIN this script :

while  (<>) {
        print "$1\n" if /\s*(\w+)\s+NS\s+.*/
       #print what found in parens if the (current) line
       # begins whith zero or more space/tab... one or
       # more letter (we save it by enclosing it in parens)
       # at least one space then the 2 letters NS followed
       # by at least a space anf maybe other char
}
[download]

will do the job.

But BEWARE I've made (far too many) assumptions here....

• NS is always uppercase (hint: see the i modifier otherwise)
• The domain name is always followed by NS (it seems to be the case in your example...)
  
• ...

Hope this helps in your regex learning...

You should may be edit your node and add some <BR> to make it more readable...