Last time I did anything with paypal I don't think they allowed sending info back to the thank you script.
But you could go around this by setting up a user data entry form before going to the paypal link, and using cookies/sessions, and even double them with sql to send the info, but i am not aware of a way to prevent them from skipping the payment and just jumping to the thank you script (how this would help them, I don't know, but someone would find a way).
but a simple setcookie would work to transfer the info, it just wouldn't be that secure
eg send script
CODE
<?
$name = $_POST['name from a form'];
$email = $_POST['email from form'];
//repeat for all info you want to transfer
setcookie("uname",$name,time()+86400) //time()+86400 sets the cookie to last a day,
setcookie("uemail",$email,time()+86400) //but you can remove the cookie in the thank you script.
//repeat for all info you want to transfer
echo "<html link to paypal and messages here>";
?>
eg recieve script(thank you page)
CODE
<?
if(!isset($_COOKIE['uname'])) {
echo "<some message about the fact that they shouldn't be here>";
} else {
echo "thank you ".$_COOKIE['uname']." for doing something";
mail( "your@email.here", "THE EMAIL SUBJECT HERE", "This is a message letting you know that ".$_COOKIE['uname']." at ".$_COOKIE['uemail]." just hit the thank you script with the info from the user info form", "From: your thank you page" );
unset($_COOKIE['uname'], $_COOKIE['uemail']);
}
?>
thats a rough example, but it should work to send you the data (provided your host allows php mailing)