The ability to control your primary machine remotely can come in rather handy when you need to access your documents and applications using your netbook or laptop. While you might be tempted to go with a solution based on the popular VNC protocol, you should keep in mind that it has two serious limitations: it's both insecure and slow. A much better solution is to use the FreeNX server and an NX client, which offers a secure connection that works well even with a slow modem link -- a boon for users on the move.
The first order of business is to install the FreeNX server software on your primary machine. To do this on Ubuntu, you have to add the FreeNX Team PPA repository to the sources.list file. Open the file for editing using the sudo nano /etc/apt/sources.list command and add the following lines to it:

deb http://ppa.launchpad.net/freenx-team/ubuntu VERSION main
deb-src http://ppa.launchpad.net/freenx-team/ubuntu VERSION main

Replace the VERSION string with the actual Ubuntu version installed on your machine (e.g., "jaunty" for Ubuntu 9.04). Save the modifications and close the file. Next, add the public key of FreeNX PPA using the following command:

sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 2a8e3034d018a4ce

Update the repository info and install the FreeNX server:

sudo apt-get update && sudo apt-get install freenx

Run then the nxsetup utility to install and configure the server:

sudo /usr/lib/nx/nxsetup --install

The setup procedure automatically starts the FreeNX server, but you can always stop and start the server manually using the following commands:

sudo /etc/init.d/freenx-server stop
sudo /etc/init.d/freenx-server start

Once the server is up and running, it's time to install NX client software on your netbook or laptop. To do this, use the sudo apt-get install qtnx command which installs the QtNX NX client.

Launch QtNX, and select Create new session from the Session drop-down list to set up a new session. Most of the fields in the configuration window are self-explanatory, so you shouldn't have any problems configuring the session. Press OK when you are done, enter your user name and password of the user account on the remote host, hit the Connect button, and you should see the remote desktop in all its beauty.