have you looked in disk managent to see if you have multiple partitions on the same disk?
10:11, 8 October 2008 (CDT)10:11, 8 October 2008 (CDT)10:11, 8 October 2008 (CDT)10:11, 8 October 2008 (CDT)~
You may want to have a look in the Recycler. I say this, because when I took over my current job, one of our servers was idle and not patched, and not firewalled. I noticed an almost 900GB discrepancy in what was clearly being used, and what was available.
I dug around, and then I noticed that the Recycler (hidden normally) had folders tucked inside it, with almost a Terabyte of foreign-dubbed DVD rips. I ended up tracking the culprit to an ISP overseas that had apparently hacked the box and was using it for remote storage.
So dig around more, someone may have hidden some files in some unlikely places on that box.