You need the System Disc/s to do this .... depending on the OS version you boot from the disc and use Disc Utilities or if it's pre-OS X it's called something else. Either way you can go into options and zero out the data which is more or less eliminating the readability of whatever was on the drive prior to you zeroing it (I'm talking about the average user being able to read it). It's usually perfectly safe to do this but beware of user error.
Yes, it is safe. Though, 9.999 times out of 10 I would say it is completely unnecessary.
The only time I would see doing it would be if you plan on selling your machine to someone else.
No, you will have a blank hard drive with nothing on it and you wont be able to boot. Assumgin you even can format your harddrive while in os x. Which I doubt.
If you want a clean install just ake a new user account, give it admin rights, then remove the old user account and profile. Thats about as clean as anyone needs.
Boot from your install disk, wipe hard drive and reinstall OS X =)
EDIT: You might even be able to do an Erase and Install with your install disk even if it's the same system you're installing. I've never tried it but I can't imagine why it wouldn't work.
Sure you could do that but why bother? The beauty of a Mac is its simplicity and there is nothing really written to the hard drive outside your user profile except some applications to the applications folder. Make a new user and delete the old and clear out your applications folder of any 3rd party programs and you have yourself a clean install and you spent 3 minutes instead of an hour.
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