Download Putty and Puttygen.exe : http://www.chiark.greenend.org.uk/~sgtatham/putty/
Follow the directions that are on the following website http://www.codelathe.com/blog/index.php/2009/02/20/ssh-without-password-using-putty/
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.