Reinstalling OSX.....

You should do a System Restore which will return your OS to its factory-shipped state. This will remove your data and user-installed applications.

 

When you are booted from the install CD, click the "Customize" button. It is on one of the menus during the installation. Just select "reformat (i believe)". It will erase everything.

 

2 ways

1. When the installer starts open up disc utility from the Installer menu. There you can reformat (quick, zero all data, or 8way reformat). Then install as normal

2. From the intall wizard select the drive you want to install to then check the box that says "Reformat Drive". This will do a quick reformat.

 

erase & install

So, if you do a "erase & install" option after restarting with the restore CD and pressing C when the Mac is booting up, does it do the clean install? I mean "clean" in a way that the fresh copy of the OS will be installed on the hard drive as if it is installed from the factory. Hard disk will be wrote from outer edge or inner edge of the disk and I am wondering "erase & install" will do the installation from the "beginning" of the hard disk instead of staring the fresh install after the old data areas on the hard disk.

 

I've got a question does it harm the harddrive if you repeatedly do a reinstall?

 

I wouldn't say it will harm your hard drive. Do remember though that your hd drive will eventually die. Everytime it spins, you just shortened its life. A reinstall is no different than a anyother hd access of the same time length, so it will shorten its life time. I don't mean 6 installs and your hd is done. We are talking 100s or 1000s or more, before it will kill your drive. Installs are not the only thing that makes your hd spin. It spins during: boot, loading a program, accessing data, using swap or virtual mem, etc. So I wouldn't worry the occasional install.