I had the same problem and I find out that the problem is caused by the file /etc/kde3/kdm/kdmrc . I use Kurumin Linux (a debian distro), and DPKG made a backup of this file, the only thing I needed to correct the fonts was to restore the backup ...
If you have the backup of this configuration file, your problem is solved. You could get with a friend that uses the same distro that you use.
I hope I had helped, and again, sorry for my writing errors ... Feel free to correct me by MP