;Option 1
on *:TEXT:!greets*:#:{ 
if ($nick isop $chan) {
    if ($2 == on) {
set $($+(%Greets.,$chan)) 
notice $nick Greets are now On for this channel.
}
    elseif ($2 == off) {
unset $($+(%Greets.,$chan)) 
notice $nick Greets are now Off for this channel.
}
    else { 
notice $nick You must be an Op in this channel.
    }
  }
}

;Option 2
on *:TEXT:!greets*:#: {
if ( $2 == on ) && $nick($chan,$nick,oh) {
enable #greets
notice $nick Greets are now On for this channel.
}
elseif ( $2 == off ) $nick($chan,$nick,oh) {
disable #greets
notice $nick Greets are now On for this channel.
}
}

#greets on
on *:JOIN:#: {
if ( $nick isreg $chan ) {
notice $nick Welcome $nick $+ , i am $me $+ , if you want me in your channel type /invite $me <your chan>.
}
}
#greets end

Note: if both don't work...forget it then.. ¬_¬