Form to mail problem

first of all im quite new to PHP but i think im starting to get it.
second, i have two two problems, both with the same kind of script.
the first script is for when a user registers with my website an email is sent to the admin (me) to let me know of their existence on the database.
the script i am using is as follows:

$sendTo = "[email protected]";
$subject = “LS12 Style!! New user registration”;
$headers = “From: " . $_POST[“firstname”] . " " . $_POST[“suranme”];
$headers .= “<” . $_POST[“email”] .”>
$headers .= "Reply-To: " . $_POST[“email”];
$message = “New user: " . $_POST[“username”] . " has registered with the LS12Style website.”;
mail($sendTo, $subject, $message, $headers);

the problem with this is that when i recieve the email the ‘from’ header only shows the first name. thats the only problem i have with that.

my next problem is with a script that sends an email to the user welcoming them to my website and thanking them for registering as well as reminding them of their login details.
here is the code i am using for that:

$sendTo = $_POST[‘email’];
$subject = “LS12 Style website registration.”;
$headers = “From: Ashley Broadley”;
$headers .= "<theashman>
$headers .= “Reply-To: [email protected]”;
$message = "Dear " . $_POST[“firstname”] . " " . $_POST[“surname”] . ",<br>Thank you for registering with the website.<br>Your login details are as follows:<br>Username: " . $_POST[“username”] . "<br>Password: " . $_POST[“password”] . “<br>Please go to <a></a> to login.”;
mail($sendTo, $subject, $message, $headers);

the problem with this block is that it doesn’t even send the email. to the email address specified in the form. i am also not sure if the html tags i have used in the $message are valid and if the email will follow the formatting i have set out.

your help is greatly appreciated.
Thanks in advance