Php cowboy...somebody help me?!

hello,

i have a flash website that uses a php file to create an email and send it to a hotmail address. Ignoring the fact that it currently doesnt work at all!!(server problems)…i have been told that it is vulnerable to spammers. I have been told that i can fix this by inserting something into a string or something but i have zero php knowledge. I have had a look on google and found a few tutorials…but have trouble following what they are talking about.
Could anyone help me?..its a fairly simple code, i just want it to be safe:

<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01 Transitional//EN” “http://www.w3.org/TR/html4/loose.dtd”>
<html>
<head>
<meta http-equiv=“Content-Type” content=“text/html; charset=iso-8859-1”>
<title>untitled</title>
</head>

<body>
<?
$name = $_POST[“name”];
$email = $_POST[“email”];
$number = $_POST[“number”];
$message = $_POST[“message”];
$to = “peterryan23@hotmail.com”;
$subject = “website enquiry”;
$msg = "$name has contacted you regarding your website. Their contact details are below:

email address- $email contact phone number- $number

";
$msg .= "Message from $name:
$message

";
mail($to, $subject, $msg, "From: jordy fu website
Reply-To:$email
");
?>

</body>
</html>