No package for any OS. (AFAIK)
But "ns-allinone-2.33" is one standalone application and easy to build.
Get the 'tar.gz' from
and extract to your preferred location e.g. /usr/local/ (or /home)
Build with command './install'
Ubuntu 7.10 will need: 'libx11-dev' and 'libxmu-dev'
Ubuntu 8.04 : the same + 'libxmu-headers' and 'libxt-dev'
To use ns2 : see addresses in 'README'
Good luck !