usb driver


I have a dual Powermac G5 with the OS X (10.4.1).
I think that I need the proper usb drivers for a usb pia or serial cable.
Here's the story:
I am trying to run a Panther Vinyl Cutter attached by a usb pia cable. I also tried a usb serial cable. The computer sees the cables (I checked in the system profiler.)
I can't get the computer and the cutter to communicate. Either the production manager (Flexipro 7.5 v5 software) says it cannot open the port, or it sends the project (a test cut) but nothing happens at the cutter.
I'm open to suggestions. I've searched (the manufacturer of the cutter) to find a solution (none there). I've e-mailed them (no response yet....). I've done the same with Scanvec Amiable (the software company). They sent me a driver, but it didn't change anything.
So, I'm open to suggestions on how to get this cutter working!!!