To the the "blurry background" pics you are talking about, you need to use low apature settings.
FYI, this term is called depth of field. The higher the apature setting (F22) will give you an all around sharp image. A lower apature setting (F3.8) will only give you a sharp image if you focus on that object. Anything else that is not focused on will be blurred (like the background in your first picture).
check this out..
http://www.cs.mtu.edu/~shene/DigiCam...-of-field.html