[NTLDR]

Find in functions.php:

PHP Code:

eval("\$retval = \"".gettemplate("postbit")."\";"); 


And change to:

PHP Code:

if ($bbuserinfo[userid]==0) { //unreg users
eval("\$retval = \"".gettemplate("postbit_unreg")."\";");
} else if ($bbuserinfo[usergroupid]==X) { //banned users
eval("\$retval = \"".gettemplate("postbit_banned")."\";");
} else {
eval("\$retval = \"".gettemplate("postbit")."\";");
} 


Untested but should work, make sure you change X to the banned usergroupid.