$result = mysql_query("SELECT * FROM authormail WHERE username='$username'");
$exists = mysql_num_rows($result);

if ($exists == 1)
{
    echo "CP BLAH BLAH BLAH"; //Show Control Panel


} 
else
//If they haven't signed up.
{
echo '<p>Welcome to the AuthorMail control panel!</p>
<p>You do not currently have an AuthorMail account, but you have the sufficient amount of AUTH$. To apply for an AuthorMail account, click <a href="http://www.authorzone.uni.cc/authormail.php?action=signup">here</a>. </p>';
}