A great tool to scan harddisk drives under Windows and show proportional usage of folder structures and files in one big picture is SequoiaView. Example image on the page.
Freeware from University Of Eindhoven, Netherlands. Unfortunately their website is in disarray. The download link goes to the German Heise.de ; publishers of computer magazine c’t and absolutely trustworthy. Click on the big green download button on the right.
What you do is you tell it the drive to scan, e.g. “C:\”; wait for the scan to complete, identify the biggest box you want to get rid of, and delete it and rescan… There are other such tools but I like the way SequoiaView displays it the best. It is named after Sequoiadendron giganteum a.k.a Giant Redwood – the developers thought the look of the images reminds of the bark of that tree.