Other posters have basically told you what you need to do differently, but I just wanted to be sure you understood why:

my %Config =( 
   PPingPath => '/home/dean/pping-v1.37/pping ', 
   PPingOptions => '-t 15 -q |', 
   TraceRTPath => '/usr/sbin/traceroute', 
   TRHops => '-m 3 | ', 
   ExternalTarget => (
      'www.microsoft.com -p 80',
      'www.netscape.com -p 80', 
      'www.silverhand.co.uk -p 80', 
      'www.demon.net -p 80', 
      'www.whitehouse.org -p 80'
   ), 
   Hosts => (
      'www.netscape.come -p 80', 
      'www.microsoft.com -p 80'
   ) 
);
[download]

This is exactly equivalent to:

my %Config =( 
   'PPingPath', '/home/dean/pping-v1.37/pping ',
   'PPingOptions', '-t 15 -q |', 
   'TraceRTPath', '/usr/sbin/traceroute', 
   'TRHops', '-m 3 | ', 
   'ExternalTarget', 'www.microsoft.com -p 80',
   'www.netscape.com -p 80', 'www.silverhand.co.uk -p 80', 
   'www.demon.net -p 80', 'www.whitehouse.org -p 80', 
   'Hosts', 'www.netscape.come -p 80', 
   'www.microsoft.com -p 80' 
);
[download]

Since the parenthesis in there the way you used them essentially just *grouping* the items, not indicating that they're an array reference, so they don't really have an effect. Note the number of arguments above are odd, which isn't valid in a hash assignment (each of the "keys" on the left and the "values" on the right), so you get that error. If you want to use a list as a "value" for