Trouble with Open flow tutorial-xterm display error and not in the sudoers file error

I am trying to do this open flow tutorial and I am completely new to networking and systems. I am a college student and I need help with this. I have finished a part of the tutorial (http://www.openflow.org/wk/index.php/OpenFlow_Tutorial) and I am able to get the "ssh -X mininet@ipaddress" command working. If i type xterm next, it is giving me a display is not set error but when I open the terminal again and just type xterm without typing the ssh -X thing, it is opening a new window for xterm. I am confused. Is that what it is supposed to do? The next part of the tutorial asks me to type "sudo mn --topo single,3 --mac --switch ovsk --controller remote" in my ssh terminal and this is what happened when i tried it.

Last login: Fri May 17 19:34:53 on ttys003

mobile-172-16-103-167:~ SHREYA20$ ssh -X mininet@192.168.56.1

Password:

X11 forwarding request failed on channel 0

Last login: Fri May 17 19:35:19 2013 from 192.168.56.1

mobile-172-16-103-167:~ mininet$ ssh -Y mininet@192.168.56.1

Password:

Last login: Fri May 17 23:46:27 2013 from 192.168.56.1

mobile-172-16-103-167:~ mininet$ sudo mn --topo single,3 --mac --switch ovsk --controller remote

WARNING: Improper use of the sudo command could lead to data loss

or the deletion of important system files. Please double-check your

typing when using sudo. Type "man sudo" for more information.

To proceed, enter your password, or type Ctrl-C to abort.

Password:

mininet is not in the sudoers file. This incident will be reported.

mobile-172-16-103-167:~ mininet$

I need to finish this tutorial soon and I need help with this. Any help would be greatly appreciated. Thank you!