First, get valid license key and Enterprise Version from their download page (use deb package), just click downloads, try it and download.
In case type
Edit /etc/vnc/config and add
-AllowedUsers=*:d -SecurityTypes=RA2
to set encrypted connection and allow users. Then start it via shell by typing vncserver and connect from another client (which has the enterprise vncviewer available).
http://www.realvnc.com/products/enterprise/4.4/vncserver.html
In X configure the vncserver to accept only VNC password if you prefer this authentication method.
Then do the startup thingy
vim /etc/rc.local
add line
su -l-c "/usr/bin/vncserver -geometry 1600x1200 -depth 24 > /tmp/vncserver.log 2>&1 &" &
and reboot. Connect to