This is a bit of a longshot, and Im almost certain the answer is no! But anyway... Is there a way to send information via the POST method without using a form? For example, I have a form that is handled by just a PHP script on its own. The information is then checked and the user is then redirected back to the form page using a redirect header. The page then states whether or not it was all successful. The thing is, I would like to be able to send the form information back to the webpage so that the invalid fields can then be highlighted. Is there a way to do this in the way that I need? Or will I just have to set the form to submit to another form where the invalid fields are then highlighted? Does that make sense?

It can be done with JavaScript, as part of an AJAX request. Here is a thread I found about it: http://www.webmasterworld.com/forum91/4960.htm

Here is a simple way to do it with jQuery: http://docs.jquery.com/Ajax/jQuery.post

Unfortunately, JavaScript can be disabled. Since POST requests are made from the client, I'm not sure there is another way to do it.

To answer your main point, Php's cURL function http://uk2.php.net/curl will enable you to send POST data without a form.

The script below will send the variables $first_name and $last_name within the $_POST superglobal array just like a form would.

PHP Code:

<?php
 $ch = curl_init('http://mysite.com/post_to_script.php');
 curl_setopt ($ch, CURLOPT_POST, 1);
 curl_setopt ($ch, CURLOPT_POSTFIELDS, "first_name=Joe&last_name=Bloggs");
 curl_exec ($ch);
 curl_close ($ch);
?>

Although looking at your problem, your best bet would be to use a single script to handle the form and error handling. No redirect would be necessary and you wouldn't need to mess with cURL. Just have the form POST your data back to the script.

If your using PHP 5 you can use its exception model to handle errors in the submission http://uk2.php.net/exceptions.