you could also use an init sub, where you require the modules you need, and set some variables to the different subs...

note: I have not tested this code, and I haven't done any cross-platform scripting that requires something like this, I just remembered seeing this technique in Perl For System Administration by David N. Blank-Edelman (ORA).

sub Init {
    use Common::Module;
    my ($common_var01, $common_var02) = ($foo, $bar);

    if ($^0 eq "MSWin32") {
        require Win32::Baz;
        require Win32::Quux;

        common_sub01 = "common_sub01_nt";
        common_sub02 = "common_sub02_nt";
    }
    else {
        require Foo;

        common_sub01 = "common_sub01_unix";
        common_sub02 = "common_sub02_unix";
    }
}

sub common_sub01_nt {
    ...
}

sub common_sub01_unix {
    ...
}

# main program
# (where we call the subs)
&$common_sub01($foo, $bar) if $foobar;
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hope it helps,