IBOOK G4 reset or HDD wipe

Greetings all,
A friend of mine recently gave me her old Ibook G4. I have virtually no interest in it myself, but I told her i'd get rid of all the personal information on the HDD. I am a total PC guy for all my life so I know nothing about the MAC operating system. I have the following questions:

1.) Is there a utility or program out there for the IBOOK that will do any kind of OS wipe, like delete all personal information and return the OS to a factory state

2.) If not, is the OS on the IBOOK G4 free? I typically format HDD's and install windows but I have to pay for windows. I don't know if Apple works the same or if the OS for this might be downloadable.

I basically just want as close to fresh OS as possible, I am going to put it in EBAY to sell it.

Thank you

You need the install discs that came with that computer, or a retail version of the OS required to do so.
If you don't have the install discs, go to the Apple symbol, about this Mac, and it will tell you what OS is on it.
If you click more info and tell us the specs or the model number, then we can tell you whether you need panther (OS X 10.3.x) or tiger (OS X 10.3.x).