HELP sharing usb external hd through mybook to view media!

hey, i’ve a mybook 1t and i want to share another 500g external hd over the network by connect it into the usb.

the external hd i have is just full of movies and i want to be able to view them through twonky to play on xbox etc

i’ve enabled sharing in twonky, which says the usb drive will be read straight away etc etc but its not.

does anyone know how to set up what i’m doing?