An easy way to install Eclipse on Ubuntu is through the Ubuntu repositories. This can be done by opening up the “Ubuntu Software Center” under Applications. Click on Developer Tools -> IDEs. Then look for Eclipse from the list of IDEs that shows up. If you click on Install, you will be asked to enter your user password then it will automatically install Eclipse for you. It should be pretty straight forward here. After installation is complete, you can start Eclipse in Applications -> Programming -> Eclipse.
Another way is to install it manually by downloading the Eclipse files from http://www.eclipse.org/downloads/. You will need to install JRE or JDK first before you can run Eclipse. You can do this by typing this in the terminal.
sudo apt-get install sun-java6-jre
Extract the Eclipse files to the /opt directory so that other users can have access to it.
tar xzf eclipse-SDK-3.5.2-linux-gtk.tar.gz
sudo mv eclipse /opt/eclipse
Then create an eclipse executable in your path.
sudo touch /usr/bin/eclipse
sudo chmod 755 /usr/bin/eclipse
sudo gedit /usr/bin/eclipse
Then type in the followings and save.
Then create a gnome menu item.
sudo gedit /usr/share/applications/eclipse.desktop
Enter the following and save.
Now you can run Eclipse from Applications -> Programming -> Eclipse. You can also install different Eclipse packages for example the Eclipse + PDT package by using the manual way of installing.