The latest version of ns-2: ns-2.35 has been released.
Download ns-allinone-2.35
The official website can be found on this link: http://nsnam.isi.edu/nsnam/index.php/Roadmap#Release_schedule
The download link given above is of ns-allinone-2.35-RC4 package. The platform support is yet to be tested.
But ns-allinone-2.35-RC2 has been tested on Ubuntu Karmic, Ubuntu 8.04, Fedora 12, etc.
For more information please visit the official website here.
Hope it helps.
Regards,
Mohit P. Tahiliani