[assassingod]

Open showthread.php and find:

PHP Code:

if ($noshutdownfunc) { 


Above add:

PHP Code:

if ($bbuserinfo[posts] < 20)
{
eval("standarderror(\"".gettemplate("error_notenoughposts")."\");");
} 


(You can change 20 to whatever you want)

Create a new template called 'error_notenoughposts' with the contents:

You do not have enough posts to view this thread

Keep in mind that the only way users will be able to post is via threads