PHP Single page contact form not working

Question 1

There were two things wrong with your code.

This line:

if($_SERVER['Request_Method'] != 'POST') {

Request_Method must be in uppercase REQUEST_METHOD because it is a superglobal

And the dollar $ in front of mail()

$mail($emailto, $subject, $message, $header);

which should be:

mail($emailto, $subject, $message, $header);

Reformatted and working PHP/HTML form

<?php
if($_SERVER['REQUEST_METHOD'] != 'POST') {
    $self = $_SERVER['PHP_SELF'];
?>
<form method="POST" action="<?php echo $self; ?>">
    <table>
        <tr>
            <td style="width:100px;">
                Name:
            </td>
            <td>
                <input style="width:150px; height:25px;" placeholder="First Name" type="text" id="custname" name="custname">
            </td>
        </tr>
        <tr>
            <td>
            </td>
            <td>    
                <input style="width:150px; height:25px;" placeholder="Last Name" type="text" id="cust2name" name="cust2name">
            </td>
        </tr>
        <tr>
            <td>
                Email:
            </td>
            <td>                
                <input style="width:250px; height:25px;" placeholder="Example@domain.com" type="text" id="custemail" name="custemail">
            </td>
        </tr>
        <tr>
            <td>
                Subject:
            </td>
            <td>
                <input style="width:250px; height:25px;" placeholder="RE:Appointment & Contact" type="text" id="textsubject" name="textsubject">
            </td>
        </tr>
        <tr>
            <td>                
                Message:
            </td>
            <td>
                <textarea id="custtext" name="custtext" placeholder="Please enter your message here..." rows="6" style="resize:none; font-family:arial; width:500px; height:75px;"cols="25"></textarea>
            </td>
        </tr>
        <tr>
            <td>

            </td>
            <td>
                <input type="submit" value="Send"><input type="reset" value="Clear">
            </td>
        </tr>
    </table>
</form>
<?php
} else { 
    $name = $_POST['custname'];
    $email = $_POST['custemail'];
    $text = $_POST['custtext'];
    $subject = $_POST['textsubject'];
    $emailto = "email@domain.com";

    $header = "From: $name <$email>\r\nReply-To: $email\r\n";
    $header .= "MIME-Version: 1.0\r\n";
    $header .= "Content-type:text/html;charset=iso-8859-1\r\n";

    $message = "From: $name, Email: $email<br /><hr />$text";

    mail($emailto, $subject, $message, $header);

    echo "Your email has been sent, it will be proccessed within 48hours.";
}

?>

Question 2

First try to replace

$mail($emailto,...

with

mail($emailto,...

(Remove the "$")

Question 3

Not exactly answer to Your question, but some global attention / security points :).

Try to left the action empty (by default form is redirecting to the same page). Then check if every needed input was filled rather then check $_SERVER['REQUEST_METHOD'] != 'POST'. In that case You can fill in the form using the entered values.

For example, someone enters only name. Then mail is not send and values given by a user dissapear (someone must enter name once again). I would propose something like this (simple example with only one field - name)

$name = isset($_POST['custname']) ? $_POST['custname'] : '';
$name = htmlspecialchars($name); // !!!!!!!!!!!!!
if ($name != '' && your_valid_function($name)) { // && custmail test && other test
    SEND MAIL;
    header("Location: this_page"); // prevent refreshing this page and sending multiple mails
}
else {
    //Render form here, using $name with filled values, for example:
    echo "<form><input type=\"text\" id=\"custname\" name=\"custname\" value=\"$name\"></form>"; // notice $name here
}

PS. Always use at least htmlspecialchars when using POST values :). Be carefull with robots - form without captcha or some other security features can spam your mail box hard. Hope it helps.