I have a 120GB HDD that is split into a 12GB partition for Windows and a 100GB partition for Programs
On the 12GB partition, I have 6GB taken up by visible files and approx. 1.5GB allocated to System Restore... but I have only 1GB free.
That leaves a 3.5GB hole, where I have no known data, and nothing that I know how to clear out... but I need to clear out (since I haven't found a way to change the default drive to which files are saved... such as the My Documents folders)