[Help]Register page

<div class="form">
<form method="post" action="register.php?act=register" id="contact_form" >
<fieldset class="pt1 element">
<label for="name">Username: <span style="color: rgb(255, 0, 0);">*</span></label>
<input type="text" id="id" name="id" value="" tabindex="1" />
<label for="email">Password: <span style="color: rgb(255, 0, 0);">*</span></label>
<input type="password" id="ipassword" name="pass" value="" tabindex="2" />
<label for="website">Retype Password: <span style="color: rgb(255, 0, 0);">*</span></label>
<input type="password" id="ipassword" name="retpass" value="" tabindex="3" />
<label for="email">Email: <span style="color: rgb(255, 0, 0);">*</span></label>
<input type="Email" id="iEmail" name="Email" value="" tabindex="2" />

Required Fields (<span style="color: rgb(255, 0, 0);">*</span>).<br><br>
<code><span style="color: rgb(255, 0, 0);">

<?php
if($_GET['act'] == "register")
{
mysql_select_db($mydbacc);
$userid = trim($_POST['id']);
$password=trim($_POST['pass']);
$passretype=trim($_POST['retpass']);
$Email = trim($_POST['Email']);
$hash=$_POST['hash'];
$_SERVER['REMOTE_ADDR'];
if($userid=="" || $password=="" || $passretype=="" )
{
echo "You must fill all information in the Required Field!";
}
else
{
if($password == $passretype)
{
if(!ereg("^[0-9a-z]{4,15}$",$userid))
{
echo "Only letters and numbers only are allowed.Long 4 to 15 words";
}
else
{
$res = mysql_query("select * from account where name = '".$userid."' order by id desc");
if(mysql_num_rows($res) == 0)
{
mysql_query("insert into account (name,Password,Reg_date,email,netbar_ip) values ('".$userid."','".$hash."','".date("y-m-d H:i:s", time()).'".$Email."'."','".$_SERVER['REMOTE_ADDR']."')");
echo "Account successfully registered!";
}
else
{
echo "This account has been registered, please select another!";
}
}
}
else
{
echo "Password authentication is not the same as your Password";
}
}
}
?>