Very easily with XML::Twig. After fixing a typo in your posted XML code (and adding some phony 'foo' root tags):

use strict;
use warnings;
use XML::Twig;
use Data::Dumper;

my $xfile = <<EOF;
<foo>
<cat>
<channelName>CHANNEL123</channelName>
<name>CATEGORY123</name>
<shortName>TopCategory</shortName>
<description>This is TopCategory channel's Category</description>
<shortDescription>This is TopCategory channel's Category</shortDescrip
+tion>
<parentID>0</parentID>
<categoryTags>Vod;Download</categoryTags>
</cat>

<cat>
<channelName>Channel456</channelName>
<name>cat456</name>
<shortName>TopCategory</shortName>
<description>This is TopCategory channel's Category</description>
<shortDescription>This is TopCategory channel's Category</shortDescrip
+tion>
<parentID>0</parentID>
<categoryTags>Vod;Download</categoryTags>
</cat>

<cat>
<channelName>chann678</channelName>
<name>cat678</name>
<shortName>TopCategory</shortName>
<description>This is TopCategory channel's Category</description>
<shortDescription>This is TopCategory channel's Category</shortDescrip
+tion>
<parentID>0</parentID>
<categoryTags>Vod;Download</categoryTags>
</cat>
</foo>
EOF

my %cats;
my $t= new XML::Twig(
   twig_handlers => {cat => \&cat}
);
$t->parse($xfile);

sub cat {
   my ($twig, $cat) = @_;
   $cats{$cat->first_child('channelName')->text()} = $cat->first_child
+('name')->text();
}

print Dumper(\%cats);
[download]

Prints out:

$VAR1 = {
          'Channel456' => 'cat456',
          'chann678' => 'cat678',
          'CHANNEL123' => 'CATEGORY123'
        };
[download]