How about...

code:
Break On

$objFSO = CreateObject("Scripting.FileSystemObject")
$objDrive = $objFSO.GetDrive("C:")
"Drive " + $objDrive.DriveLetter + ": "+ $objDrive.VolumeName ?
"Available Space: " + FormatNumber($objDrive.AvailableSpace/1024, 0) + " Kbytes" ?
"Free Space: " + FormatNumber($objDrive.FreeSpace/1024, 0) + " Kbytes" ?
"Total Size: " + FormatNumber($objDrive.TotalSize/1024, 0) + " Kbytes" ?

...as an alternative to WMI?