There is not really any reason to add anything to the .bashrc
The binary 'ns' is hard coded to know the locations of it's libraries.
Just run a 'make install' (su or sudo) in ns-allinone-2.33/ns-2.33/,
... and 'ns' gets copied to /usr/local/bin/ , I.e. a system path.
The same for nam : Run 'make install' in ns-allinone-2.33/nam-1.13/
... to have /usr/local/bin/nam
Or use a binary nam : post #4 here ..