You can block it by adding it to the 'HOSTS' file which you'll find in C:\Windows\system32\drivers\etc
Open this file with Notepad and on a new line add the following:
127.0.0.1
www.google.com
Note that there must be at least one space between the IP number and the website name.
After adding the line, save the file.
Also, i did read somewhere that the HOSTS file must be in capital letters in order to function properly, so rename it using capitals (it does not have a filename extension, just HOSTS. Mine is in caps. and it works fine. you can block any website as long as you Know it's name (you can't use IP numbers, only a proper URL name).
Each site you wish to block must be on a new line beginning with 127.0.0.1 followed by at least one space, then the website name.
You can download a ready-made HOSTS file free from here:
http://www.mvps.org/winhelp2002/
It's already configured to block loads of unsavoury sites but you'll have to add google to it yourself.