By default in SUSE 11 when the OS boots up, it auto logs on the user that you had specified on to GNOME or KDE.

To prevent it from doing this, do the following:

1. Logon to the machine as root or a user with root previleges (or you can login as a normal user and launch Yast doing as a SU - Yast would ask you for the root password when you do this).

2. Launch Yast Control Centre

3. Go to "User and Group Management" located under "Security and Users"

4. From the list shown, highlight the user you want to disable auto logon for and click on the button with drop down that says "exper options" -> choose login settings -> uncheck  the "auto login" checkbox