xml_split has all ready been given and is probably the best choice for simple splitting; however, if you're looking to upgrade your XML toolkit, then XML::LibXML is a good choice and something along the lines of below should get you started.

#!/usr/bin/perl

use XML::LibXML;

my $file   = shift || die "usage $0 <xmlfile>";
my $parser = XML::LibXML->new();
my $doc    = $parser->parse_file( $file );

my $nodes  = $doc->findnodes( '/TheRoot/Message' );

foreach my $node ( @$nodes ) {
  print $node->toString();
}
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