This method of installing the XmlPL compiler tools is much easier if you are running a Debian based operating system such as Ubuntu or Knoppix. You must have root access to your system to install packages.
The following command will download XmlPL.org's public keys and install them in apt-get. This is necessary to avoid warnings when installing XmlPL packages.
wget http://www.xmlpl.org/xmlpl_pub_key.asc -O - | sudo apt-key add -
Edit /etc/apt/sources.list and add the following lines to the end of the file.
deb http://www.xmlpl.org/debian unstable/
deb http://www.xmlpl.org/debian stable/
You only need to do the first two steps once. Afterwards, you can get the latest version of XmlPL anytime by running the following commands.
sudo apt-get update
sudo apt-get install xmlpl
Alternatively, if you aren't comfortable with the above procedure you can download and install the .deb files from http://www.xmlpl.org/unstable/ and install them with
dpkg -i <package file>