ok got it:
First delete the change you made in newreply.php (convert it back to original) and use this HTML form in your episode pages:
-- cut --
<form enctype="multipart/form-data" action="/yourforum/newreply.php" name="vbform" method="post">
<input type="hidden" name="s" value="">
<input type="hidden" name="action" value="postreply">
<input type="hidden" name="threadid" value="3">
<input type="hidden" name="title" value="">
<input type="hidden" name="iconid" value="0">
<input type="hidden" name="parseurl" value="yes">
<input type="hidden" name="email" value="">
<input type="hidden" name="disablesmilies" value="">
<input type="hidden" name="signature" value="yes">
<input type="hidden" name="closethread" value="">
<input type="hidden" name="hiddenreply" value="">
<input type="hidden" name="signature" value="yes">
<input type="hidden" name="rating" value="0">
<table cellpadding="0" cellspacing="0" border="0" bgcolor="#555576" width="100%" align="center"><tr><td>
<table cellpadding="4" cellspacing="1" border="0" width="100%">
<tr>
<td bgcolor="#8080A6" colspan="2"><font face="verdana, arial, helvetica" size="2" color="#EEEEFF" class="thtcolor"><b>Post
Reply</b></font></td>
</tr>
<tr valign="top">
<td bgcolor="#DFDFDF"><font face="verdana, arial, helvetica" size="2" ><b>Your User Name:</b></font></td>
<td bgcolor="#DFDFDF"><font face="verdana, arial, helvetica" size="2" ><input type="text" class="bginput" name="username" value="A Kira Fan" size="25">
</font>
<font face="verdana,arial,helvetica" size="1" ><a href="register.php?action=signup">Want to register?</a>
</font></td>
</tr>
<tr valign="top">
<td bgcolor="#F1F1F1"><font face="verdana, arial, helvetica" size="2" ><b>Your Password:</b></font></td>
<td bgcolor="#F1F1F1"><font face="verdana, arial, helvetica" size="2" ><input type="password" class="bginput" name="password" value="" size="25">
</font>
<font face="verdana,arial,helvetica" size="1" ><a href="member.php?action=lostpw">Forgotten your password?</a>
</font></td>
</tr>
<tr>
<td bgcolor="#DFDFDF" valign="top" nowrap><font face="verdana, arial, helvetica" size="2" ><b>Your
Reply:</b></font></td>
<td bgcolor="#DFDFDF">
<table cellpadding="0" cellspacing="0" border="0">
<tr valign="top">
<td>
<textarea name="message" rows="7" cols="70" wrap="virtual" tabindex="1"></textarea>
<br>
<font face="verdana,arial,helvetica" size="1" ></font></td>
</tr>
</table>
</td>
</tr>
</table>
</td></tr></table>
<br>
<table cellpadding="2" cellspacing="0" border="0" width="100%" align="center">
<tr>
<td align="center"><font face="verdana, arial, helvetica" size="2" >
<input type="submit" class="bginput" name="submit" value="Submit Reply" accesskey="s" tabindex="2">
</font></td>
</tr>
</table>
</form>
-- cut --
Now your registered users can post with their usernames and passwords, while unregistered users (who should leave the password field blank!) can post with any name unless this name is already registered! Registered users are not suppose to be a "Kira Fan" any more!
Hope this helps..