sending info when using header()

[Cuban]

hi,
i have a login form that searches a mysql database for the user and checks that the password is correct. it then redirects to the main page, the problem is i want to set a cookie containing the username.
this is the code:

<?php setcookie("user","$username"); 


if((!$username) or (!$password))
{header("location:error1.php"); exit();}

$conn=@mysql_connect("localhost","admin","admin")
		or die ("connection");
$rs=@mysql_select_db("user",$conn)
		or die ("db selection");
$sql="select * from auth where username=(\"$username\") and password=(\"$password\")";

$rs=mysql_query($sql,$conn)
		or die ("query");

$num=mysql_numrows($rs);

if($num !=0)
{header("location:logged.php"); exit();}
else
{header("location:error2.php");}
?>

if i do it this way it , it does not set the cookie.
ive tried seperating the cookie of

<? setcookie ("user","$usename"); ?>
<? .....rest of code...... ?>

but it comes up with the error "headers already sent"!!

Please help

[laserlight]

This might be easier to see:

<?php
setcookie("user", "$username");

if ((!$username) or (!$password)) 
{
	header("location: error1.php");
	exit();
}

$conn = @mysql_connect("localhost", "admin", "admin")
	or die("connection");
@mysql_select_db("user", $conn)
	or die ("db selection");

$sql = "select * from auth where username=\"$username\" and password=\"$password\")"; 
$rs = @mysql_query($sql, $conn)
	or die ("query");

$num = mysql_num_rows($rs);

if ($num != 0)
{
	header("location: logged.php");
	exit();
}
else
{
	header("location: error2.php");
} 
?>

I would suggest testing without setting the cookie first.
Does it work?
If not, check for whitespace at the top.

[Cuban]

hmmm, think i found the problem.
when running the script on an xp machine with iis php 4.1.2 it works fine.
when runnin it on my server (win 2k with iis and php 4.1.2) it doesnt work

GRRRRrrrr!!!!