I too faced the same problem recently (when I was switching back and forth between kdm and gdm)
I restored by login window fonts by the following method.
- the login window themes for kubuntu was in /usr/share/apps/kdm/themes/kubuntu/
- the heart of the theme was kubuntu.xml
- sudo vi kubuntu.xml
- decrease the font size (in my case decreased it to 8)
- restart the display manager
- yo! it worked.
I too faced the same problem recently (when I was switching back and forth between kdm and gdm)
I restored by login window fonts by the following method.
- the login window themes for kubuntu was in /usr/share/ apps/kdm/ themes/ kubuntu/
- the heart of the theme was kubuntu.xml
- sudo vi kubuntu.xml
- decrease the font size (in my case decreased it to 8)
- restart the display manager
- yo! it worked.