Adding a user and login from "X"

[Mark Ryden]

Hello,
  I run fedora 12 with gnome. By default, I boot into gnome with Xwindows.
  When I add a user ("useradd xyz"), I see that user in the login
dialog immediately
  after boot. (there is a list of all users in the system).
  I sometimes add some users for tests, like "test1", "test2",..., "test10".
  Is there a way to prevent specific users (like "test1","test2") from
showing up in this dialog ?

Rgs,
Mark