WMI can retrieve information about drives easily. This will get you the drive information for your local machine (use -ComputerName to access a remote system):
To limit the results to only hard drives, and only those hard drives that have less than a given amount of free space, try this:
$limit = 80GB Get-WmiObject -Class Win32_LogicalDisk -Filter "DriveType=3 and Freespace<$limit" | Select-Object -Property VolumeName, Freespace, DeviceID
