I've been playing around this weekend with PowerShell and the Win32_Volume WMI class and have written some PowerShell scripts to exploit this class.
To get the volumes on a system is trivial:
$volumes = Get-WMIObject Win32_Volume
This returns an array of volume objects which you can iterate through and display. To display the whole collection, or to just see the first volume, you could do this:
You can also use a method to determine how badly fragmented a volume is, and another to run a defrag pass on a volume. Look here for a script to display a defrag analysis of the C:\ and here to actually defrag the disk.
The Win32_Volume WMI class is not available on all versions of Windows - I ran the scripts on a Longhorn B3 server.