Vista - USB External Hard Drive Spin Down

Please, I have a question(s) about my external (USB) Maxtor Personal Storage
3200 Disk Drive and how to "re-enable" it to spin down after a fixed period
of time related to inactivity. When I initially installed the drive it did
spin down after a period of inactivity. It would, logically, only spin up if
you opened Explorer or when the Backup Utility started. I don't think I made
any changes to the OS that would cause this issue? Please see the following
list related to what I have checked so far.

1. I use the MS Backup utility included as part of my Vista Ultimate
installation and that runs once a week.
2. I have the "Power Options" set to "High Performance" via the app in
Control Panel.
3. The "Advanced Options" tab under "Power Options" shows that the Hard
drive setting is set to "Turn off after 20 Minutes". I suspect that this may
only apply to the internal hard drive?
4. I don't see any options related to power under the "Properties
Dialog", related to the external hard drive, while in Explorer.


Thanks for your help!
David