My way to make the DisplayLink light up in Snow Leopard 64-bit
 

1) Use the VMware Fusion to setup a windows system. I am using winxp in the VMware.
2) Connect your DisplayLink to the usb, and let the VMware have the connection to the USB device.
3) Before you connect the monitor to the DisplayLink, setup the windows driver in VMware first.
$) ...all of you will know the reset

Try it out, enjoy.