Q:How can I use FreeNX with Ubuntu?

EDIT: For those who don't know what FreeNX is, freeNX is a remote desktop protocol, like VNC. Unlike VNC, FreeNX compresses at the X protocol level, giving it a much better experience over low-bandwidth (and high bandwidth) line. To give you an idea of FreeNX's power, I can use Smooth Scrolling in Firefox over a dial-up line without excessive jerking. Over cable/dsl lines, you can barely notice that you're not actually at the system.

It's not in Ubuntu's repositories, but is available for Debian. Add the following line to your /etc/apt/sources.list

deb http://kanotix.com/files/debian/ ./
The repository is for Kanotix, a Debian/SID Knoppix derivative.

Run apt-get install freenx.

Then, run nxsetup. If you want a nomachine key (RECOMMENDED FOR SIMPLICITY), run nxsetup --setup-nomachine-key instead. Please google the command and read the security implications of doing so! (Basically if FreeNX is flawed, there's a possibility of gaining SSH access as the NX user remotely!)

Make sure that SSH is running for FreeNX to work properly.

**Newer (like these) versions of FreeNX no longer need a nxserver --adduser command. Any user that can log into the system via PAM can log in remotely with NX. Running the nxserver --adduser commands is harmless though.

There are also nxclient deb's in the repository, so browse it and enjoy!
Important Note!
The repository also contains up-to-date reiser4progs (a good thing if you want to try reiser4, and doesn't affect you if you don't use reiser4 at all)
It also has a newer java-package that supersedes Ubuntu's. The Kanotix java-package works perfectly on Ubuntu, so not really a problem either. Just a heads-up in case you wanted to stay as purely Ubuntu as possible!

UPDATE: As someone pointed out, Kanotix FreeNX now depend on libpng being newer or equal to 1.2.7. Warty has version 1.2.5.

You can always grab the Hoary version of libpng. http://archive.ubuntu.com/ubuntu/pool/main/libp/libpng3 and friends are in Ubuntu's repository.