I'm a linux newbie myself but this problem is well known to me.
The problem is that from version 9, Red Hat has included Native Posix Thread support (NPTL). So for KDE to work, you have to patch the standard kernel source for this.
I have installed kernel 2.4.22 myself and know how to patch it and with what, but I do not know for 2.4.21. I'm sure you can find it on the internet.
Let me know if you still want to know the procedure I followed for 2.4.22.