I don't think you are on 10.6.8. That looks like the System Information screen from Lion or Mountain Lion. If you are asking about that purple area called Backups, that is local backups temporarily stored by Time Machine. If you turn Time Machine off then back on, it will zero out that space. Or you can just ignore it. If you need the space for user files, OS X will shrink the temp backup space used automatically.
Just click the Time Machine icon in the menu bar and select Open Time Machine Preferences. Then on the left side you will see an on/off button. Just turn it off then back on and go back to check, and you will see that backups purple is now close to zero.