php cookie not getting set from cookie newbie

Hi, I am trying to teach myself about cookies and using them for user authentication. I got the following code from the Wrox (Professional PHP Programmig) text (which is great) but cannot get it to set the cookie - any suggestions would be much appreciated. (Cookies is turned on as I can get it to work with a simple count cookie) This is the login file (login.php3 that the login form calls): ___start of login.php3____ <?php require 'includes/functions.php3'; if(authenticateUser($form_user_id, $form_password)){ setcookie("user",$form_user_id); setcookie("passwd",$form_password); header("Location:http://$HTTP_HOST/$doc_root/modify/modify_sam.php3"); exit(); }else{ header("Location:http://$HTTP_HOST/$doc_root/modify/error1.php3"); exit(); } ?> ___end____ and this is the functions file that is referenced above: ___start of functions.php3____ <?php require 'includes/common.php3'; //function authenticate user function authenticateUser($user, $password) { global $db_server,$HTTP_HOST,$db_login,$db_password,$db_name,$doc_root; //open a persistent connection with the MySQL server if(!($link=mysql_pconnect ($db_server,$db_login,$db_password))){ DisplayErrMsg(sprintf("internal error %d:%s\n",mysql_errno(),mysql_error())); return 0; } //do the password/user authentication if(!($result=mysql_db_query("$db_name", "SELECT * FROM user_profile WHERE user_id='$user'"))){ DisplayErrMsg(sprintf("internal error %d:%s\n",mysql_errno(),mysql_error())); return 0; } //compare results if(($row=mysql_fetch_array($result)) && ($password == $row["password"] && $password != " ")) return 1; else return 0; } ___end___ the common.php3 (referenced above) just has the db stuff in it, that you don't need to see. The authenticate part works in that it will only let people in that have used the correct sign in and password, but it is not setting a cookie (browser does not alert me), and then when they get to the edit page it will not authenticate them again but rather lets any one in. the first page of the edit screen ie., after being authentcated (but without the HTML that follows after the PHP), is: ____start of modify_sam.php3____ <?php require 'includes/functions.php3'; //check for authentication if(!authenticateUser($cookie_user, $cookie_passwd)){ header("Location:http://$HTTP_HOST/$doc_root/modify/login.html"); exit(); } //Connect to the database if(!($link=mysql_pconnect($db_server,$db_login,$db_password))){ DisplayErrMsg(sprintf("internal error %d:%s\n",mysql_errno(),mysql_error())); exit(); } ?> _____end____ So everytime a user trys to login the get a "bad login screen" if the incorrect login is used (correct) but if the correct one is used, they end up back at the login screen as they are not authenticated when they reach modify_sam.php3 because the cookie has not been set. Any suggestions on where I am going astray here, or some good web references would be much appreciated. Cheers Stuart