This is an obvious candidate for substr(). The following code just takes the substring of every pair of sequential characters and replaces each set with the reverse of that substring, effectively swapping the 2 characters.

#!c:/perl/bin/perl -w
$|++;

use strict;

my $word = 'jigglewort';

for my $i (0 .. length($word)-1) {
  my $tmp = $word;
  substr($tmp, $i, 2, reverse substr($tmp, $i, 2));
  # _or_
  # substr($tmp, $i, 2) = reverse substr($tmp, $i, 2);

  print $tmp, "\n";
}

=for output
ijgglewort
jgiglewort
jigglewort
jiglgewort
jiggelwort
jigglweort
jiggleowrt
jigglewrot
jigglewotr
jigglewort
=cut
[download]

Update: Added lvalue substr as an option :)