RESOLUTION
At the first Plesk deb repository should be added into the sources list.Main link to the Plesk Debian repository is http://autoinstall.plesk.com/debian/.You can open it in the browser to see what Plesk versions are available.
Now add the repository record for needed Plesk version into /etc/apt/sources.list, for example the line below is for Plesk 8.2.1 for Debian 4.0 Etch:
deb http://autoinstall.plesk.com/debian/PSA_8.2.1 etch all
Next run update to cache packages list:
# apt-get update Now you can install Plesk. For example to install base Plesk package use:
# apt-get install psa