Hi Devil,
Try this script and see if this is what you are looking for.
NOTE username, username 1 and username 2 should be replaced with what usernames you want and the custom greetings you want. Let me know if this works, I haven't tested it. Also take note, your brackets cannot be placed together like you have them.
on !*:JOIN:#: {
if ($nick == username) { msg $chan This is user's greeting. }
elseif ($nick == username1) { msg $chan This is user2's greeting. }
elseif ($nick == username2) { msg $chan This is user3's greeting. }
}
