USB Hub stops sleep mode

Hi

I have a PC with Vista Home Premium (the motherboard is an ASUS A7V8X).
I recently got a 7 port USB Hub for it (Trust brand). When I plug it in
now, whenever I try to send the PC to sleep, it goes into sleep mode and
then immediately comes back out of sleep mode back on again!!

If I unplug the hub, sleep mode works fine.

Anyone got any ideas as to why this is happening?

P.S. If this is the wrong NG to post to, please let me know where I
should be going

Thanks in advance...

Isaac