I prefer to use Treesize Free (http://www.jam-software.com/treesize_free/) to see what the HD looks like.
From what i see you have a HUGE collection of AIFF & WAV files. I'm guessing you are editing a lot of audio files? Right there you have nearly 30 Gigs of data.
There are different ways to look at how much space is taken by a file (file size <> Space taken on HD). I.E. A file which is 513 Bytes in size will actually take up 1024 byes of space on the Hard drive. This is due to how Windows allocates space. This is a complicated subject to explain. In short, I believe the programs are looking at space in different ways, hence the difference in space.
Windows has a folder named WinSxS which can grow rather large in size over time (http://support.microsoft.com/kb/2795190). Your windows folder shows 19 gigs which is not bad. I'm more concerned about your User profile(s) being so large.
Have you ran the windows Cleanup util?