Get used/free space on entire hdd w/ multiple partitions?

I've got a windows 7 laptop w/ 3 internal hard drives --

is there a way to configure the status bar in dOpus to do this? I've studied thru the help section
that pertains to the status bar & tool tips, but can't figure that out yet.

I searched for a "freeware disk space" type utility, but none I found/used seem to do what I want:

Give me the used & Free space for the entire drive, which contains multiple partitions --
they all seem to only give data for each individual partition.

In "My Computer" top level window, I selected my 13 partitions on the disk in question,
but the status bar only gave a TOTAL used/free space for all 3 drives.

And, if dOpus can't do this, would someone kindly point me to either an app that will,
or a command line that will? Thanks very much ~

You should be able to add that as a column to the Computer folder, using a script. It's not something Opus has out of the box.