An quick and easy install of freenet requires sun java. Here are 3 easy steps to set it up on Ubuntu Dapper.

1. Make sure you have acces to the multiverse part of the Ubuntu packages. To do this you can add a line like this

   	deb http://archive.ubuntu.com/ubuntu/ dapper multiverse

   
   to your /etc/apt/sources.list file and run sudo apt-get update.
   
   Or if you feel more comfortable with it you can choose Administration --> Software-Sources from the System menue, check the box Copyright restricted software (multiverse), then click Close and Reload.
   
   
2. Install the sun jre package. This can be done by issuing the command

   	sudo apt-get install sun-java5-jre

   
   Or if you want to use Java 6:
   

   	sudo apt-get install sun-java6-jre

   
   
3. Make sure the sun jre is your default java. This can be done by issuing the command

   	sudo update-alternatives --config java

   
   (Please notice that this will change the default java for all users of the PC, and their programs. You can change it at any time by doing sudo update-alternatives --config java )

You should now have sun java properly installed. Now you are ready to install freenet! Follow this guide for the installation
FreenetInstallationLinux