KDE 4 unable to lock screen or switch user

[Chris Gow]

Hi all:

Running KDE 4 on Kubuntu 7.10 I can not lock the session, nor can I switch 
users. Attempting to lock the session blanks the screen and presents me with 
a dialog that says: Unable to lock the session, reason: No appropriate 
greeter configured. Where do I configure said greeter?

When I attempt to switch users, I get presented with the runner applet. Not 
quite what I had in mind.

thanks

-- chris