I dont have ftp access at the mo but it should just be a case of an simple if statement on the attachment.php file ill ahev a look later on but it would prob be something along the lines of
PHP Code:
if ($bbuserinfo[postcount]) <= x {
normal code for download
}
else
{
nopermission();
}
Im going by memory here so not sure on the exact query if not a bit of SQL will get the postcount but this will absiclyl not allow them to download anywhere in the forums if they have less that a certain postcount as for individual forums that would be a little more tricky