WQL – PCs with more that 2 GB free on C:

select distinct
    SMS_R_System.Name,
    SMS_G_System_LOGICAL_DISK.*
from 
    SMS_R_System inner join SMS_G_System_LOGICAL_DISK on SMS_G_System_LOGICAL_DISK.ResourceID = SMS_R_System.ResourceId
where
    SMS_G_System_LOGICAL_DISK.FreeSpace > 2048
    and SMS_G_System_LOGICAL_DISK.DeviceID = “C:”
order by
    SMS_R_System.Name