I have been using Gnome and just installed KDE4. I can’t figure out how to switch to the KDE environment.
From what I’ve read on this forum, I’m supposed to have an option on the login screen where I can choose my DE but I don’t have that option.
What now?
Disable auto-login via Yast - Security And Users - User group management
Expert options
you may need to reboot
Check this re;kde4
http://forums.opensuse.org/how-faq-read-only/unreviewed-how-faq/414532-kde4-2-how-add-guide.html#post1986169
Auto user login in is already disabled.
I also have the kde/42 repo added to YAST. It was added by the one click install. Do you think something didn’t go right with the install of KDE?
Some users seem to experience problems at the login window if using gdm. If I was you, I would login to Gnome as normal. Then use YaST /etc/sysconfig editor to change display manager from gdm to kdm. Navigate to Desktop → Display manager → DISPLAYMANAGER
Alternatively, you can edit /etc/sysconfig/displaymanager directly (as root) and change this line
DISPLAYMANAGER=“gdm”
to
DISPLAYMANAGER=“kdm”
Now when you login you can change session to KDE as required.
Thanks. That worked.
You’re welcome 
Make sure you have a look around this forum re KDE 4.2. (Don’t use the earlier KDE 4.1.X version). Lots of posts discussing this.