Well let's see....
Is the form passed directly to your PHP file? Nothing happens in between like a verfication file or something that echo's the data back to the user?
If this is the case it's possible you may have to declare the variables agin using
<input type="hidded" name="variable_name" value="$variable_name">
where variable_name is what ever variable your dealing with i.e. $email.
Pending everything is right in your php.ini file (mainly global variables is on) then there is no reason for a form not to pass the variables directly to the ProcessScript.php.
I would try doing it this way....
File below is your form.html
<form name="ProcessScript" action="ProcessScript.php" method="post">
<input type="text" name="Name">
<input type="text" name="Email">
</form>
Below is your ProcessScript.php file
<? php
$msg .= "This person wants to join your newsletter list\n\n"
$msg .= "Name:\t$name\n";
$msg .= "E-mail:\t$email\n";
$recipient = "subscribe@mysite.com";
$subject = "Subscription Request";
$mailheaders = "From: \t $name<> \n";
$mailheaders .= "Reply-To: $email\n\n";
mail($recipient, $subject, $msg, $mailheaders);
?>
try putting these two formats together and see if you get your variables through in your email.