Proper way to disconnect from Internet during new product install

I will be installing NIS 2010 tomorrow and just want to be clear on proper way to disconnect from the internet when doing the uninstall and new install

I have heard conflicting methods

Some say disconnect dsl line from phone jack, some say disconnect phone line from DSL modem, others say disconnect computer ( ethernet?) line from modem

Are any of these ways relatively equally the same and its just a matter of preference?

 

here is my set up

 

Desktop PC> DSL Modem (Not modem/router)>phone jack

 

thanks in advance