Basically it's the same procedure as in secure_it's tutorial for Nessus 3.2.1

http://forums.remote-exploit.org/showthread.php?t=20221

Download packages
Nessus-4.0.0-ubuntu804_i386.deb
NessusClient-4.0.0-ubuntu804_i386.deb

As you can see I've installed the Ubuntu NessusClient package and you'll get some dependency problems with a solution further down in thread. (Don't bother with the debian package. You'll get the same result - missing dependencies)

dpkg -i Nessus-4.0.0-ubuntu804_i386.deb

Configure the certificate

# /opt/nessus/sbin/nessus-mkcert

Add admin user

# /opt/nessus/sbin/nessus-adduser

register here to get the activation key

# /opt/nessus/bin/nessus-fetch --register 'here goes your key'

Now before installing the client you need to install some missing dependencies

apt-get install libqt4-core libqt4-gui libqtcore4 libqt4-network libqt4-script libqt4-xml libqt4-dbus libqt4-test libqtgui4 libqt4-svg libqt4-opengl libqt4-designer libqt4-assistant

(all in one line)

dpkg -i NessusClient-4.0.0-ubuntu804_i386.deb

# /etc/init.d/nessusd start

And start the client from the Menu>Intenet>NessusClient or use the CLI

Enjoy!