I know this is an old question, but I recently had to setup Chirp again on a new computer and have long since lost the driver CD that came with my cable... thus I was having the same problem. The issue is that it's not really a USB cable per say. What your computer is doing is emulating an analog COM port through the USB cable, and it has to have special instructions (i.e. software drivers) that tell the hardware (the USB port) how to do that.
I solved it by going directly to the Baofeng website driver page. They only have one driver installation for Windows, and although I am using Windows 10 and you asked for Windows 7, they have this note:
*Includes the following version of of the Windows operating system: Windows 7, Windows Server 2008 R2 and Windows 8, 8.1, Windows server 2012 R2, Windows Server 2016 and Windows 10
What you will need to know is if your dad's computer is running off of 32 bit or 64 bit software. Your computer will not run the opposite type. Also, make sure you download the setup executable file (link on the righthand side) and not the link under the "Processor Architecture" table, as that file is really just the source code for the drivers. I doubt you want to compile the drivers yourself!
Once I installed the drivers, I just restarted Chirp and the USB appeared as a COM port when I tried to export to the radio.