Sure would be nice if someone would do some kind of hdparm for Windows! So we could tell our hard drives to spindown, etc...
You can run hdparm under Cygwin. Or, find a standalone version for Windows 2000/2003/XP at http://hdparm-win32.dyndns.org/hdparm/
Or google "hdparm windows".
Both of those give you hdparm 6.9 which is broken in a few ways (such as always reporting the drive is in the standby ATA state.) The hdparm 9.31 source reports that it's compatible with windows, but the user needs to build it themselves. Maybe it fixes some of the issues on 6.31