[kawe]

First
You need security token your account in vBulletin Forum
different forum different security token
for check please copy paste this code to your address bar browser.

PHP Code:

javascript:alert(document.getElementsByName('securitytoken')[0].value); 


After that
you must create new HTML page ( XAMPP must be ON )

PHP Code:

<form action="http://www.yoursite.com/newreply.php?do=postreply 
name="vbform" method="post" onsubmit="return vB_Editor['vB_Editor_001'].prepare_submit(0,5)" target="_blank">
Message<br />
<textarea name="message" id="vB_Editor_001_textarea" rows="10" cols="60" style="display:block; width:540px; height:250px" tabindex="1" dir="ltr">
</textarea><br />
Security token<br />
<input type="text" name="securitytoken" value="" /><br />
<input type="hidden" name="do" value="postreply" />
Thread number<br />
<input type="text" name="t" value="" /><br /><br />
<input type="submit" value="submit message" /> 


Fill thread number with number in /showthread.php?t=xxxxxxx