use warnings;
use strict;

my $have_tie_registry = defined eval
    q{ use Win32::TieRegistry Delimiter=>"/"; 1 };
if ($have_tie_registry) {
    print "Have module\n";
    our $Registry;
    my $IEKey = $Registry->{'HKEY_CURRENT_USER/Software/'
        .'Microsoft/Internet Explorer/Main/'};
    print "<$_>\n" for keys %$IEKey;
}
else {
    chomp( my $err = $@//'unknown' );
    die $err if $^O eq 'MSWin32';
    print "On $^O, don't have module (reason: '$err')\n";
}
print "Continuing program...\n";

__END__

#### Linux:
On linux, don't have module (reason: 'Can't locate Win32/TieRegistry.p
+m in @INC (you may need to install the Win32::TieRegistry module) (@I
+NC contains: ...) at (eval 1) line 1.
BEGIN failed--compilation aborted at (eval 1) line 1.')
Continuing program...

### Windows:
Have module
<...>
<...>
...
Continuing program...
[download]

(Update: Note that as opposed to several of the other solutions here, this uses slightly different logic: if Win32::TieRegistry is available, it is used no matter which OS this is being run on; otherwise, if it's not available, that's only a fatal error if this is being run on Windows. Of course that logic can be changed, my point was mostly to show the my $have_module = eval q{ use Module; 1 }; technique.)

See also:

• Use 'use' in foreach
• The "right" way to make your script run with old versions of perl
• Bug in eval in pre-5.14
• Module::Load::Conditional