One of the software tools I use quite often client systems is SpaceMonger. SpaceMonger is a tool for keeping track of the free space on your computer. It shows graphically the size of each folder and file on your computer.
Each file or folder on a given drive is displayed in a box in the main window whose size is a relative comparison to all the other files in your system. So, for example, if the "Windows" box takes up 90% of the screen, the "C:\Windows" folder and all its sub-folders and files are taking up 90% of your "C:" drive.
SpaceMonger runs on Windows XP, Vista and Windows 7 RC1.
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