Westell/Fujitsui FDX305 USB Modem won't train

Hi

My parents-in-law have bought a new computer (USB 2.0 and SIS chipset, not
Via).

They have plugged in their existing Westell/Fujitsui FDX 305 modem,
installed the drivers, but the modem won't train.
It tries to train for a split second then reports no signal.

I have installed the modem on my computer and it works fine (USB 1 and Via
chipset!).

Anyone got any ideas?
I have seen some reports stating a USB 2.0 cable is required. Can anyone
comment on this?

We are already using the latest drivers..

Thanks

Darren