Using Putty without a Password

First

Download Putty and Puttygen.exe : http://www.chiark.greenend.org.uk/~sgtatham/putty/

Second

Follow the directions that are on the following website http://www.codelathe.com/blog/index.php/2009/02/20/ssh-without-password-using-putty/

or

http://www.howtoforge.com/how-to-configure-ssh-keys-authentication-with-putty-and-linux-server-in-5-quick-steps

Note: 
1. The authorized_keys file content should start with the "ssh_rsa" keyword followed by a space.
2. The mumble-jumble characters of the public key should be on one line (right after the space).
3. Sometimes the default home directory of a user is changed to a different path make sure that you add the .ssh and authorized_keys to the new path.