Welcome to LQ.
bash: ./install: Permission denied
May be you unpacked the tarball ns-allinone-2.34.tar.gz as root ?
Which is wrong.
No ns2 commands are meant to be run as root (or with sudo).
Suggest : Delete ns-allinone-2.34/, and start from scratch :
If one shell script has wrong permissions or isn't executable,
there can be a lot more corrupt files.
P.S. : The install command ..
cd ns-allinone-2.34/ && export CC=gcc34 CXX=g++34 && sh install