Well, you should probably use the "Vista" drivers off of the CD. When you open Device manager, when you plug in and unplug the cable, you should see the device appear and disappear. If it isn't appearing as a COM port, you need to go into its properties (when plugged in), select "UPDATE DRIVERS", then point the computer to the appropriate file or directory on the CD.
If it does appear as a COM port, confirm which COM port it is being assigned to and ensure that is the one you are selecting in whichever software you are using.