[ubuntu-in] installation problem

[paramveer sran]

i m trying to install ns-allinone-2.34 on ubuntu 9.04 and getting the
following errors. i m proceeding by using the following commands:
$ cd / media/disk
$ tar -xvf ns-allinone-2.34.tar.gz
then
$sudo apt-get install build-essential autoconf automake libxmu-dev
param at ubuntu:/media/disk$ sudo apt-get install build-essential
autoconf automakelibxmu-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package build-essential
plz help me how can i install build essentials
thanx