Yes, you can definatly use any usb to 9 pin serial cable. Here's the problem that I had tho, Your computer probably doesn't have the proper driver installed for that cable. Mine didn't. And none of the PCIIIr software includes that driver either.
But dont worry, even the cheapie $12 cable from frys has the driver included on a disc inside the package. Get that installed before you hook up power commander.
Once you get the PC talking to your computer, you may need to go into the com port menu of the PC software command bar. I just had to try selecting available ports one by one until one worked (I think mine used com port 8).
Hope that helps? If you have specific computer questions I'll try to help cause it drove me batty trying to figure it out.
btw, radio crap tried to send me out the door with their most expensive gold-plated cable. He rung it up-$52. nonono
John, 2000 RC51 #000100