Double the desktop, not double the fun!
 

Used YAST and based on a recommendation in one of the Linux magazines, I installed xfce - and like it!

However, now when I boot up or log in on my laptop I get both KDE and xfce loading, which means a warning on "there is already a taskbar running" and some confusing screen effects.

I 'm sure this is simple, but I haven't found where to specify which desktop is to load automatically, so I can start with one or the other (I know I can log out and log back in with another desktop, but that is a pain to do after waiting for everything to load)

Maybe you need to disable the autologin feature in the login manager via kcontrol.

I can't find an auto-login feature to disable in kcontrol. There is no login manager showing. Also, I'd like to be able to log in automatically, but in either kde or xfce, not both....

Yes its there. Kcontrol -> System Administration -> Login Manager -> Convenience. I am not sure the KDE autologin feature will enable you to boot into XFCE instead of KDE, but I am sure if you search around you will find a solution.