This link will help:
Also, if you have a very large capacity HDD, try reducing the amount of space taken up by System Restore.
It's set at 12 per cent by default but this was in the days when HDD capacities were much smaller.
My own 60GB HDD is set, for instance, at three per cent for System Restore.
IIRC Diskkeeper Lite and the Windows defrag utility are basically the same.