I have no driver on windows for the usb device. libusb provides some sort of generic driver so that the usb device can be accessible to qemu. At least this is how I understand it.[/QUOTE]
Its the other way around.
The virtual machine (host) provides an environment to the guest OS that mimics hardware. The host virtual machine program provides the device descriptions that are passed to the guest OS. The USB devices can be created, simulating a device that can be set up with the generic Windows USB drivers.
I use virt-manager and kvm and the created VMs have USB devices by default. I assume qemu can do the same.