Hmm, I would try this:

Start by basically getting rid of kdm and xdm:
Code:
apt-get --purge remove xdm
Code:
apt-get --purge remove kdm
Then reinstall whichever you pefer:
Code:
apt-get -t unstable install kdm
One caveat, you might not be able to log in as root from the login screen with the latest version of kdm, that can be changed, I don't remember the file that needs to be edited , there are other posts dealing with it on this forum.

Also, if you want to get kde running from a console login type startx, once logged in.

HTH