[PHP] Help! Can't set cookie or redirect!!!

[Phil Powell]

I am getting the following errors attempting to set a cookie and redirect:

Warning: Cannot add header information - headers already sent by (output started at 
/users/ppowell/web/my/process.php:5) in /users/ppowell/web/my/process.php on line 76

Warning: Cannot add header information - headers already sent by (output started at 
/users/ppowell/web/my/process.php:5) in /users/ppowell/web/my/process.php on line 77


Lines:

   setcookie("valLayout", $id, time()+3600*24*30*12*100, $SERVER_NAME); // WILL EXPIRE 
IN 100 YEARS.. UM YEAH
    header("Location: " . $HTTP_POST_VARS["refURL"]);

The first time I ran this script it set the cookie just fine; subsequent runnings of 
this script produce this error.  What am I doing wrong, anyone?

Thanx
Phil