Unfortunately it is not anymore possible through package management. Searching for openoffice in Synaptic Package Manager or apt-get, you will find openoffice but it will install libreoffice not openoffice. Only way, as I know currently, is install by hand.
To installation we need package and you can get it from here http://download.openoffice.org/other.html
$ tar xvfz downloaded_file.tar.gz $ apt-get remove libreoffice*.* $ dpkg -i unpacked_dir/DEBS/*.deb $ dpkg -i unpacked_dir/DEBS/desktop-integration/*.deb