Safest way to connect a virus affected Pen drive

My cousins run stationery and recently have brought a Xerox cum printing machine. They also have a computer to connect pen drives of customers basically. system has been formatted multiple times because of virus attack. My main guess is that due to frequent connection of pen drives and hard disk the PC might be getting virus attacks. So, I want to help them. Can anybody list the precautions one can take to securely connect a pen drive to PC, safely browse the contents of pen drive and print them without harming their own computers?
