Using FC3, I *strongly* suggest using yum, otherwise one day your box is going to be borked.
Setup your repositories, then: yum groupinstall KDE.
If you don't have yum, go here,
find a mirror and drill down till you find in the FC3 section, keep drilling till you reach the rpm section.
get the yum rpm and
fedora-release-3-8.i386.rpm (yum repositories)
yum will install the original KDE that came with FC3 using the base repositories (above).
Or go here;
and learn how to get the latest KDE version.
Other site you should visit;
Being on the net you will want to;
# yum update