Shouldn't I have more Free Space?

It seems like my files are somehow taking up more room on my drive
than what they should.

Here's the situation. My C: drive indicates that I my "Used Space" is
113 GB, but when I select all the files and folders (even the hidden
system files/folders) and right click to view properties, I see that
the selected files take up about 62 GB. Where's the remaining 51 GB
coming from?

I figured it out. Turns out it was caused by Vista's previous version
feature. I had copied a large number of files to the wrong location
and then moved them to the proper location. The previous version
feature must have saved a copy of those files. Since this is a new
computer, there really isn't any danger in deleting the previous
versions (under the "more options" tab within the "disk cleanup"
window). Once I did this, about 40 GB was returned to me.