this is the tutorial
http://ubuntuforums.org/showthread.php?t=441496
and ...-> error

root@ubuntu:~/freenx# dpkg -i nxserver_2.1.0-22_i386.deb
(Reading database ... 88873 files and directories currently installed.)
Preparing to replace nxserver 2.1.0-22 (using nxserver_2.1.0-22_i386.deb) ...
Unpacking replacement nxserver ...
Setting up nxserver (2.1.0-22) ...
NX> 704 ERROR: Cannot add user: nx. User: nx already exists.
NX> 704 ERROR: Please try to fix the problem by reinstalling the server.
dpkg: error processing nxserver (--install):
 subprocess post-installation script returned error exit status 1
Errors were encountered while processing:
 nxserver
root@ubuntu:~/freenx#