The first time you try using the XTL software, your computer should install the drive it needs. I always start the computer, start the XTL software and then connect the programming USB cable to the computer. Make sure the cable is connected to the radio control head before you connect it to the USB port. If you use this sequence, the computer should install the required driver all by itself.
Every now and then on a new computer install of the software, I get out of sequence. If this happens, the best thing to do is just re-boot the computer and start over.
Then once you get the software started, don't forget to set the connection to the USB selection. Otherwise, it won't ever see the radio.