I just found this at the KDE site.  Maybe it is the reason that you have not 
yet been successful?  I don't have time to try it this morning but I will 
tonight or tomorrow.

http://download.at.kde.org/pub/kde/stable/3.0/Red Hat/README

I says you should delete the previous version RPMs before installing the new 
ones and has the command lines to use.

Alan