Which returns a reference to the hash (I think),

In perl, "quotes create strings" , so you have a string not a reference -- ditch the quotes -- and you're off to review perlintro :)

Thanks so for your help! Unfortunately being able to read the documentation is certainly not a guarantee to understanding it.
Regards,
Smaug.
_{Peddle faster monkeys!! I need more power!!}

In my experience, XML::Simple makes dealing with very simple XML simple but it makes dealing with more complex XML quite difficult. Had you spent two days learning one of the alternatives (I use XML::LibXML almost exclusively these days, but there are other very capable modules that give you good control over both parsing and generation of XML files) you could probably have solved your problem and learned a more powerful tool for future work.

In summary, my suggestion is to use XML::Simple if it does what you need by default or you can tweak it in a few minutes. Otherwise, invest in learning a more general/powerful tool.

Update:

As an example of one way to get your hash with XML::LibXML:

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

my $xml = do { local $/; <DATA> };
my $dom = XML::LibXML->load_xml(string => $xml);

my %vendors = map {
       $_->getAttribute('vendorUniqueKey') => $_->getAttribute('name')
    } @{$dom->getElementsByTagName('Vendor')};


print Dumper(\%vendors);

__DATA__
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Import format="3.0" fileId="54630000-3141-1404-4310-7F0000014030" fil
+eCreationDateTime="2012-07-23T06:04:31.415" catalogSource="TLCMz">
    <Catalog>
        <Vendors>
          <Vendor name="Allen Systems" vendorUniqueKey="ALLENGRP"/>
          <Vendor name="Aonix North America" vendorUniqueKey="AONIX"/>
          <Vendor name="Beta Systems Software" vendorUniqueKey="BETASY
+S"/>
          <Vendor name="BMC Software" vendorUniqueKey="BMC"/>
        </Vendors>
    </Catalog>
</Import>
[download]

gives

$VAR1 = {
          'BETASYS' => 'Beta Systems Software',
          'BMC' => 'BMC Software',
          'ALLENGRP' => 'Allen Systems',
          'AONIX' => 'Aonix North America'
        };
[download]

That's simple enough. The problem is, reading all the XML::LibXML docs (there are many) to find out how to do this isn't so simple.

If you've got a reasonably recent version of XML::LibXML, that can be made even simpler.

use XML::LibXML 1.94;
use Data::Dumper;

my %hash = XML::LibXML
    -> load_xml(location => 'mydata.xml')
    -> getElementsByTagName('Vendor')
    -> map(sub { $_->{vendorUniqueKey} => $_->{name} });

print Dumper \%hash;
[download]

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

Building on the correction by Anonymous Monk above, the following code gives you a hash in which each entry has a vendorUniqueKey as the key and the corresponding name as the value:

#! perl
use strict;
use warnings;
use Data::Dumper;
use XML::Simple;

my $xmldoc  = XMLin("dsys.xml");
my $vendors = $xmldoc->{'Catalog'}->{'Vendors'};
my %vendors = %{ $vendors->{'Vendor'} };
my %unique_vendors;

while (my ($outer_key, $outer_value) = each %vendors)
{
    if (ref($outer_value) eq 'HASH')
    {
        my ($inner_key, $inner_value) = each %$outer_value;

        if ($inner_key eq 'vendorUniqueKey')
        {
            $unique_vendors{$inner_value} = $outer_key;
        }
        else
        {
            warn "Inner key is not 'vendorUniqueKey'";
        }
    }
    else
    {
        warn "Outer value is not a hash reference";
    }
}

print Dumper(\%unique_vendors);
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Output:

$VAR1 = {
          'BETASYS' => 'Beta Systems Software',
          'BMC' => 'BMC Software',
          'ALLENGRP' => 'Allen Systems',
          'AONIX' => 'Aonix North America'
        };
[download]

HTH,

If you want to use XML::Simple, then this is also one possible solution

my %resulting_vendors;
my %vendors = %{ $xmldoc->{Catalog}{Vendors}{Vendor} };
foreach my $vendor2 (keys %vendors )    {
    print "vendorUniqueKey: [", $vendors{$vendor2}{vendorUniqueKey}, "
+], vendor2: [$vendor2]\n"; 
    $resulting_vendors{$vendors{$vendor2}{vendorUniqueKey}}=$vendor2;
}
print Data::Dumper->Dump( [\%resulting_vendors], [qw(resulting_vendors
+)] );
[download]

The advantage of this code is, that it only uses things that you also used

The line

my %vendors = %{ $xmldoc->{Catalog}{Vendors}{Vendor} };
[download]

isn't really necessary, you can freely use the right part instead of %vendors, if you really want.

See Simpler than XML::Simple for some reasons why you should not use XML::Simple and what to use instead.

As we do not know what do you need the data for, I can only guess in what format would you like them so just a tiny example. This code specifies that form each &lve;Vendor> you want the vendorUniqueKey as the key and the name as the value and then lets you execute some code to process this data once the </Vendors> tag is parsed. This style lets you process huge files without keeping everything in memory.

use strict;
use XML::Rules;

my $parser = XML::Rules->new(
    stripspaces => 7,
    rules => {
        Vendor => sub {return $_[1]->{vendorUniqueKey} => $_[1]->{name
+}},
        Vendors => sub {
            my ($tag, $vendors) = @_;

            print "We have " . scalar(keys %$vendors) . " vendors\n";
            foreach (keys %$vendors) {
                print " $_ => $vendors->{$_}\n";
            }
            return;
        },
        ':default:' => ''
    }
);

$parser->parse(\*DATA);

__DATA__
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Import format="3.0" fileId="54630000-3141-1404-4310-7F0000014030" fil
+eCreationDateTime="2+012-07-23T06:04:31.415" catalogSource="TLCMz">
    <Catalog>
        <Vendors>
          <Vendor name="Allen Systems" vendorUniqueKey="ALLENGRP"/>
          <Vendor name="Aonix North America" vendorUniqueKey="AONIX"/>
          <Vendor name="Beta Systems Software" vendorUniqueKey="BETASY
+S"/>
          <Vendor name="BMC Software" vendorUniqueKey="BMC"/>
        </Vendors>
    </Catalog>
</Import>
[download]