You could use one of the free services. There are sites like www.Bravenet.com who have those sorts of things. If you want to do it your self using php would work.
[EDIT]
An example of using php and saving to a text file is:
mailing.html
mailprocess.php:
The Text file should conatin all the emails registered with a ':' separator.
[EDIT]
An example of using php and saving to a text file is:
mailing.html
<HTML> <HEAD> <TITLE>Mailing List</TITLE> </HEAD> <BODY> <FORM METHOD="POST" ACTION="mailprocess.php"> Email: <INPUT TYPE="TEXT" NAME="email"> <INPUT TYPE="SUBMIT"> </FORM> </BODY> </HTML>
mailprocess.php:
<?php $email = $_POST["email"]; $file = fopen("emails.txt", "a"); fwrite($file,$email."/n"); fclose($file); echo("Thanks, you have been subscribed"); ?>
The Text file should conatin all the emails registered with a ':' separator.