i have run this program exactly as you've typed it...

i get the same error:

 Can't locate object method "new" via package "Net::Ping" at ...

could there be something wrong with the module?

magnus here is the exact code block:
(imagine, if you will, Net::Ping has already been called)

sub reachable { 

     (@machines_to_ping) = @_; 
     $host = Net::Ping->new(); 

     foreach (@machines_to_ping){ 

          $reachable = $host->ping($_); 

               if ($reach == 1){ 
                  print "$_ reachable\n"; 
               } else { 
                  print "$_ not reachable\n"; 
               } 
      } 
}
[download]

hopefully this helps...