Yup, you're correct, you can't have duplicate keys.. and you haven't.. try this..

sub display {
  print '-' x 30,"\n";

  foreach my $key (sort (keys (%hash))) {
    printf("%12s is now number %d\n",$hash{$key},$key);
  }

  print '-' x 30,"\n";

  foreach my $key (sort keys %hash) {
    print "$key = $hash{$key}\n";
  }

  print '-' x 30,"\n";
}
__END__

prints:
------------------------------
       angel is now number 1
       buffy is now number 2
    cordelia is now number 3
        dawn is now number 4
       ethan is now number 5
             is now number 5
       faith is now number 6
       giles is now number 7
------------------------------
1 = angel
2 = buffy
3 = cordelia
4 = dawn
5 = ethan
54 =
6 = faith
7 = giles
------------------------------
[download]

cheers,

J