It sounds to me like your PC is adequate. I recently upgraded my pc and now am using a USB cable. I remember having a tough time setting up a serial cable. I bought it from a man in Colorado. His website was: http://www.milehighwings.com/

Maybe you could look at his site, or email him and see if he still has instructions for setting up a serial port cable. His site does show how to set up a usb cable at: http://www.milehighwings.com/manual_usb.htm

Here is another link with setup and instructions for your cable. I bought my USB cable from this person.

http://www.tti-us.com/sim/

I will look around and see if I still have the instructions for setting up the Serial Cable.