Slow Imac G4


I have an Imac G4, it almost 3 yrs old and is now one of the lower spec models, i am running Panther on it and currently have 9 gigs of space left on the hard drive. My mac seems to have slowed down dramatically and its performance is not what it used to be.

Any idea's on how to improve things?! I have heard about rebuilding the desktop and zapping the PRAM as well as dfreagging the drive but if so, are there any tools i can get for this?