package Foo::Bar;

use strict;
use warnings;

use parent "Foo::Bar::$^O"; # will die here for any OS not yet supported

1;

=pod

Documentation here

=cut

##</code><code>##

package Foo::Bar::MSWin32;

use strict;
use warnings;
use parent 'Foo::Bar::base';

use Win32::OLE;

sub frob
{
    Win32::OLE->...
}

# ...

1;

##</code><code>##

package Foo::Bar::unixoid;

use strict;
use warnings;
use parent 'Foo::Bar::base';

sub frob
{
    # do it without Win32::OLE
}

# ...

1;

##</code><code>##

package Foo::Bar::linux;
use parent 'Foo::Bar::unixoid';
1;

##</code><code>##

package Foo::Bar::solaris;
use parent 'Foo::Bar::unixoid';
1;

##</code><code>##

package Foo::Bar::cygwin;
use parent 'Foo::Bar::MSWin32'; # assuming you can use OLE with cygwin - never tried it
1;

##</code><code>##

package Foo::Bar::base;

use strict;
use warnings;

sub new
{
    my $proto=shift;
    my $class=ref($proto)||$proto;
    my $self=bless {},$class;
    $self->init(@_) or die "init() failed";
    return $self;
}

sub init
{
    # ...
}

sub some_generic_function
{
    # ...
}

1;

##</code><code>##

use Foo::Bar;

my $f=Foo::Bar->new();
$f->frob('bla','bla');
$f->some_generic_function();