[ns] difference between ns-2.34 and ns-2.26

[Jyotirmoy Karjee]

Hi ,
       I have some doubt with ns- version ?

     (a) what is the difference between ns-2.34 and ns-2.26  version ??

      (b) If  i install both the version ns-2.34 and ns-2.26 in my linux
system , is there any problem while running the
            script file ??

   with regards
   Jyotirmoy