Erasing HD of old iMac

Excellent, the boot into the Mac OS using the install disc that came with the computer. Then open Disk Utility on the DVD and erase the internal HD. It is EXTREMELY unusual that someone still has the original media so congratulations for being so careful!

Your computer is WAY WAY WAY too old. You have 2 choices.

1. Use the original DVD disc that came with the computer and boot the computer using that and use Disk Utility to erase the HD.
2. The next option is the physically remove the HD.

You cannot erase the internal HD from the startup HD unless you have Mac OS 10.6.8 or later installed on it.

It did not erase everything, the only way to fully erase the HD on Tiger 10.4.11 is with the original DVD that shipped with the computer. I suspect you do not have that still. If I am correct then you should remove the internal HD (or have someone do it for you) and then physically destroy the HD.

What to do before you sell, give away, or trade in your Mac - Apple Support

You would follow the steps in What to do before you sell, give away, or trade in your Mac

I have a 2007 iMac that I am going to recycle. I see this reply that says if I have Mac OS 10.6.8 or later installed, I should be able to erase without the original disks. Could someone please describe how to do this? I have Mac OS 10.7.5 Thanks

We don't know what you did so how can we answer the question? When you post, please be specific as we cannot look over your shoulder.

Your welcome.