SpaceControl is designed to be simple. Download the application, unpack the file and drag the application (the one with the hard disk icon) to your Applications folder. Launch SpaceControl. A text will appear in your menu bar showing how much free space there are available on your startup disk. Klick on the menu item and submenus will appear, showing information about all disks or volumes mounted on your desktop.
If you want SpaceControl to start everytime you log o to your Mac you can choose that option in the Preference window. You can also make some choises about how you want the menu item to appear.
What will SpaceControl do if I run out of free space on my startup disk?
SpaceControl will warn you when the free space available on your startup disk goes below the choosen limit.
You can change the limit at which you get a warning, in the Preference windows. When you break that limit, SpaceControl will warn you by changing the color of it's text in the menu and also put up a messagebox to warn you.