I'm guessing that you're using the variables $name and $ok in your script instead of their proper names $POST['name'] and $POST['ok'].
Having $name automatically have the value of the 'name' field in the form is considered a Bad Thing these days, and PHP is supporting it less and less (and may stop altogether).
Obviously, the Windows 2000 implementation you're using still uses the old behaviour, and the Linux box the new one.