Try to delete (or better rename) the .kde folder in your homedirectory. You will then get the default settings on the next session. I am not working on Linux roght now, so I can't tell you which file it is in detail, but if you've freshly set up your system, you probably won't loose too many settings if you delete all.
EDIT: You were too fast to find the solution yourself
I guess as a normal user, you cannot delete the default settings, just hide them. The defaults should be located in /opt/kde3/share/config, your custom settings in a similar path in your home directory (/home/user/.kde/share/config), but I am not sure about that (see above).