Do you have to have a library card to use the computers to print something out

No you do not

From the library website: The prints are in black and white and cost 10¢ per page. Guest Passes can be obtained from the Information Desk. A Guest Pass is only good for one day. Guest Pass users cannot set appointments for later in the week - the guest pass expires at the end of the day it is made. Library Card users can set appointments later in the week. Patrons can have only one appointment scheduled at a time (multiple appointments are not allowed).