Have you ever run low on hard drive space and not been able to figure out where it all went? Windows has never had any built-in way to easily find folders hiding lots of large files. Folder Size for Windows provides that ability.
To install Folder Size, open your web browser and go to http://preactiveit.com, then click on "Utilities" at the top of the site. When the page loads, look for "Folder Size for Windows". Below it will be a link to download it. The install is a simple one. Choose "Typical" install and click "Next" a few times.
Once Folder Size is installed, open "My Computer" and double click on the C: drive. Click on "View", then on "Details". Near the top of the window you should see column headers like "Name", "Size", etc. Right click on one of those headers and left click on "Folder Size" when the menu appears. This makes the "Folder Size" column appear. If you do not see the "Folder Size" option on the menu when you right click, reboot your computer and try it again. This column will slowly fill in with folder sizes. Allow a few minutes for it to finalize those numbers.
To find where you have lots of data, open the largest folder. You will have to show the Folder Size column again as you open each sub folder, but you can keep opening the largest folder until you find the culprit. If you are having disk space problems, you will likely find that one or more users have a large store of downloaded music or movies.