I use Perfectdisk, and this allows me to shut down the PC after a defrag.
You have to create a schedule, so I just create one that starts in one minute.
You can set which HDDs to defrag if you have more than one, which method to use, and the most important, shut down windows when finished.
I find it invaluable too, for those overnight defrags.
HTH,
Vin.
EDIT: Using it in Vista x64 with no problems too, just for the record.