The variables in Win32::Registry are exported to the main name space, so in your program you need to do something like:

use strict;
use Win32::Registry;

package myPackage;
print $::HKEY_LOCAL_MACHINE; # not $HKEY_LOCAL_MACHINE
[download]

By the way, Win32::Registry is obsolete, the doc suggests one to use Win32::TieRegistry

Updated: I went to look at the code in Win32::Registry.pm, and found the following segment, which should explain this issue pretty well.

#define the basic registry objects to be exported.
#these had to be hardwired unfortunately.
# XXX Yuck!

{
    package main;
    use vars qw(
        $HKEY_CLASSES_ROOT
        $HKEY_CURRENT_USER
        $HKEY_LOCAL_MACHINE
        $HKEY_USERS
        $HKEY_PERFORMANCE_DATA
        $HKEY_CURRENT_CONFIG
        $HKEY_DYN_DATA
           );
}

$::HKEY_CLASSES_ROOT        = _new(&HKEY_CLASSES_ROOT);
$::HKEY_CURRENT_USER        = _new(&HKEY_CURRENT_USER);
$::HKEY_LOCAL_MACHINE        = _new(&HKEY_LOCAL_MACHINE);
$::HKEY_USERS            = _new(&HKEY_USERS);
$::HKEY_PERFORMANCE_DATA    = _new(&HKEY_PERFORMANCE_DATA);
$::HKEY_CURRENT_CONFIG        = _new(&HKEY_CURRENT_CONFIG);
$::HKEY_DYN_DATA        = _new(&HKEY_DYN_DATA);
[download]