When you try to modify your host file in Vista an error message will display. In order to modify the HOSTS file you will have to run Notepad as an Administrator.
1- Go to Start > All Programs > Accessories
2- Open the Accessories folder and right click Notepad
3- Click Run as administrator
4- Click Continue button inside the User Account Control dialog
5- Click File > Open and go to C:\Windows\System32\Drivers\etc
6- Click on the filter drop down menu (bottom right corner) and select All Files
7- Select Hosts and click Open
8- Make your changes, save and close Notepad