I suggest you to wait until Mandrake releases rpm for a newer version of KDE.
To get the latest KDE, you have to compile it, which may be difficult for a newbie.
Antoher solution is to go to kde.org and download the most recent rpm. You just have to select what you need in the download area. There are no rpms built for Mandrake 9.1, but I suppose those for Red Hat will work.
****Please take advice that I don't know much about Linux, so I may have made errors in my suggestion. If someone sees an error, please correct me now!