In my experience, USB ID's are defined in the kernel driver itself (in a struct usb_device_id), and on inserting a usb device, the usb system probes the driver if it thinks it supports it (which I think assigning a udev rule for the IDs helps with).
However, if no driver is found that supports the given vendor and product IDs, then a driver for the device will not be loaded, and hence never found in ifconfig.
Searching a fairly recent kernel source I have lying around (3.3.0), there doesn't seem to be any USB ids listed for this vendor, and definitely not in the plusb driver (drivers/net/usb/plusb.c) - only VIDs 0x067b (prolific) and 0x050d (Belkin) are listed. So there's no chance that this device will work with this kernel (and probably not with the one you're using too).
I suggest that you either have a go at getting the source for your kernel and adding your device IDs to the plusb driver ID table, if you're happy doing that, or searching/posting on the USB/netdev kernel mailing lists to see if the device is known and getting a developer to add the device to the correct driver...I realise this may be out of your comfort zone though!