I have upgraded to KDE4 on Debian Lenny
(using the testing and unstable repos.
Aptitude installed e.g.
The Debian login screen comes up but tells that
the kde session type is no more valid.
The only session types available are Default, twm, TWM, Failsafe.
However if I login with twm and do
it shows that kdm is running!
BTW I ran kaboom and selected original KDE4 settings