Where has my HD space gone?

[chameleon]

I have a Vertex 3 SSD as my main drive. Its formatted space is 111GB.
It is currently reporting 17GB (93.8GB used) free. I have added up the folders that are listed on my C drive and they only come to about 50GB. My pagefile is only around 200MB so that isn't using it up. Where has all my HDD space gone? I am using Win 7 home.

 

[Culinia]

http://windirstat.info/index.html

 

[chameleon]

OO, ta for that. seems a lot of it is used up with Syswow64, which for some strange reason seems to be filled up with about 16GB of World Of Warcraft stuff, even though I have that installed on my other hard drive???