Prevent an outside form from being submitted

[brooksh]

I have two scripts.

Form1.php is a standard submission form that has

<form name="Form1" method=POST action="Form2.php">
<input name="domain" type="text" size="20"/>
<input name="username" type="text" size="20" />
<input name="password" type="password" size="20" />
<input name="email" type="text" size="20" />
<input type="submit" value="Create">

Form2.php creates a new account with post functions.

$domain = $HTTP_POST_VARS['domain'];
$username = $HTTP_POST_VARS['username'];
$password = $HTTP_POST_VARS['password'];
$email = $HTTP_POST_VARS['email'];

The problem is that I can create Form1.php somewhere else and submit it and it works. How can I prevent someone from creating their own Form1.php and submitting it to Form2.php and creating a new account?

[planetsim]

There are a couple of possibilities probably the best is to create a Session probably on the page that displays the form. When the form is submitted check that the Session exists if not more than likely a user has tried from another location.