There is an absolute easy way to install ubuntu. Let us see step by step procedure to install ubuntu by using ubuntu windows installer.
First download the windows installer by writing following in google and open the first link.
Now, Once the Windows installer has been downloaded, you need to open it to install Ubuntu.
Select the drive, give username and password.
Now, your download and installation begins as shown in the following diagram. It may take a while depending on your speed.
After its completion, you will see the following figure.
Click finish. And there you go. Enjoy.
So, this is the easiest way to install ubuntu. Now, if you want to install ns2 , the easy way, you can use Ubuntu Software Center for that. It provides with ease to install different softwares by wizard.