I had a similar problem, although I think my problems started when I upgraded to KDE 3.2 (can't remember, to be honest, whether I had already messed with the KDE fonts before I upgraded from 3.1.x to 3.2), but this is how I fixed it.
Look in the .qt folder in your user's home directory (for me /home/brett/.qt), and open qtrc in an editor.
Remove the line that says:
(assuming it exists)
If it is there, remove it, save the file, restart X, and that should fix things. It did the trick for me. Hope it works for you.