use XML::Rules;
my $parser = XML::Rules->new(
  stripspaces => 3,
  rules => {
    'ID,value' => 'content',
    field => sub {$_[1]->{ID} => $_[1]->{value}},
    page => 'as array',
    root => sub {$_[1]->{page}},
  }
);
my $data = $parser->parse(\*DATA);

use Data::Dumper;
print Dumper($data);

$data->[1]{Comments} = "many, of various quality";

# on the other hand the output is rather crazy. We have to convert the
+ data structure to a format containing all the tags.
print $parser->ToXML(root => {page => [map {
    my $fields = $_;
    +{field => [map { +{ID => [$_], value => [$fields->{$_}]} } keys %
+$fields]}
} @$data]}, 0, '  ');

# or, if I split it down a bit:
print $parser->ToXML(root => {page => [map { hash2fields($_) } @$data]
+}, 0, '  ');

sub hash2fields {
    my $fields = shift;
    return {field => [map { +{ID => [$_], value => [$fields->{$_}]} } 
+keys %$fields]}
}


__DATA__
<root>
  <page>
   <field>
     <ID>fname</ID>
     <value>Jenda</value>
   </field>
   <field>
     <ID>lname</ID>
     <value>Krynicky</value>
   </field>
  </page>
  <page>
   <field>
     <ID>Site</ID>
     <value>PerlMonks</value>
   </field>
   <field>
     <ID>Nick</ID>
     <value>Jenda</value>
   </field>
  </page>
</root>
[download]

A little easier to access and modify the data (plus the data structure takes up less memory), the output is a bit scary. Use Data::Dumper to have a look at the structure passed to ->ToXML() to see how it works, it's quite similar to what XML::Simple produced.

P.S.: If anyone has a clever idea how better to specify the datastructure->XML mapping I'm all ears.

Update: I posted a meditation regarding the output at Datastructures to XML.