1) First, turn off any unnecessary Start Up Services (daemons).
In Linux and Unix in general, daemons are system processes that run in the background without requiring any intervention from the user's side. They are started on boot via files in /etc/rc.d/init.d and provide certain services. The more you have running the longer it will take to boot. Your system will also run slower running unnecessary services in the background.
To modify your startup services open the Mandrake Control Center - System - Services and unselect those that you feel you do not need, you can click on the "info" button for a brief description of the service and you can also go here for more info.
2) Speed up your hard drive. For details, click here .
3) If using KDE:
A nice option in KDE is the multiple desktops, however each desktop loads it's wallpaper etc.. into memory. If you don't use this option go into the KDE Control Center - Look n Feel - Desktop and change the number of desktops to 1.
Upgrade KDE to version 2.2.2. KDE squashed many bugs in this upgrade and improved speed and performance. Download it from www.kde.org
KDE is a very memory intensive GUI, If you have less than a Pentium II processor and 128MB of ram KDE is going to be very slow. If upgrading is not an option, try one of the less demanding GUI's like Gnome or Blackbox, their not as pretty but their fast.