If you want to display and change your CPU frequency under Ubuntu 11.04 (Unity), then use the CPU Frequency indicator.
So, open the Terminal and run these commands:
sudo add-apt-repository ppa:artfwo/ppa
sudo apt-get update
sudo apt-get install indicator-cpufreq
To start this indicator applet, run simply this command via the Terminal:
Or create a launcher on your desktop using the same command. Once launched, an icon will be displayed in the notification area, click it to view proposed CPU frequencies: