a. Unless you have a serial port on your PC - new ones don't - you will need to purchase a USB-serial converter. Uniden sells the USB-1, and it's available from Scanner Master
b. You will need to install drivers so that your PC recognizes the scanner as a valid device. This article will describe the steps you will need to follow - it's set up for XP, but you should be able to figure out where to go using this as a guide. Note that anything in blue is a link, both here and in our wiki
At the bottom of the article is a link for the Uniden TWiki - it has a link for the Prolific website where up to date drivers may be found
c. While we don't have the instructions for the 996XT for allocating and configuring the 2 ports, we do have them for the older 996T, and I'm willing to bet they are nearly the same.
Here is the link to some brief descriptions of the procedure...