Multiple Instances of the same capture card not recognized

I have four Sabrent USB-AVCPT capture cards running under Windows 7, each attached to a camera. I have attempted to attach 4 of them at a time so that I can open four instances of a video-chat program--one for each camera. The problem is that the program will only recognize one of the cameras. When using a Gigaware USB hub, it will recognize two, because for some reason port 2 gives one of the cameras a different designation from the other three. I was wondering if there was a way to get different designations from the hardware so that the program I'm using recognizes them separately? I've tried renaming aspects of the registry, which either doesn't work or (more likely) I didn't do it correctly. Does anyone know how to do this, or can point me toward a tutorial that will allow me to do this?

This is likely a driver issue.

You could try throwing in a couple USB-PCI adapters and attach one camera to each adapter and see if you can get them recognized that way.