In order to install NX 3.5.0 on a Slackware distributions, you need to install the compressed tar packages of NX Client, NX Node and NX server.

To install NX, extract  as follows:

# tar -C /usr/ -xzf nxclient-3.5.0...
# tar -C /usr/ -xzf nxnode-3.5.0...
# tar -C /usr/ -xzf nxserver-3.5.0...

Then, create the following directories:

/etc/init.d/
/etc/rc#.d/    where # is 0 through 6

Next,  install node and server by running:

# /usr/NX/scripts/setup/nxserver --install redhat
# /usr/NX/scripts/setup/nxnode --install redhat

Finally, place the following in /etc/rc.local

'/etc/init.d/nxserver start'

As KDE is not in the "standard" location, you can use the following settings in the NX Client GUI (3.5.0) to start a KDE session:

General -> Desktop Settings -> Unix -> Custom

Run the following command:
/opt/kde/bin/startkde

Options:
New Virtual Desktop