@Mohammed

few things to clear other things for you :

1- dnsspoof or ettercap dns spoof plugin cannot redirect a website to another ex : google.com to talk.maemo.org
it doesn't work like this

2-it can redirect to a local ip
ex : talk.maemo.org to 192.168.1.55 (a random selected ip addres or your IP)
so if you want to block others in your office from accessing a website
you will need to redirect them to an empty local ip
or to your ip for some needs like (activating apache2 server and put an index.html than says : this site is blocked or so)

or (the one i love) activate a metsploit browser exploit and redirect them to your local ip and they get hacked

3- you cannot do any of this if you are using cable (mostly all offices do so)
to arp spoof someone: You and he MUST be using wireless

as for the way using them: http://google.com

hope this helps