Plug the cable into a USB port, then go to the device manager under computer properties, click on hardware>device manager>com ports and see what port the cable is assigned too.
If the cable is assigned to a port higher then 4 or NOT SHOWN at all, you need to do one or both of a couple of things.
If the cable is shown but on a high port number, you need to reassign it to port 2, 3, 4 and MAYBE 5 as the program does not like to work on ports over 5.
If the cable is not showing at all, then you do not have the driver loaded. Go to proflic.com and down load PL2303 and load it.
Then recheck you port assignment.
As for the Windows, you do not need to use 98, the program works just fine on XP, Vista and 7 but do not try on 8.