Target Disk Mode -- Heeelp!!

I just installed a new unformatted HD in my 5 year old laptop. I'm trying to reinstall Mac OS on it. When I use my Leopard drop in disk, the installer comes up and says i can't install because i dont have tiger on it. when i use my tiger install disk, nothing comes up -- it just flashes the question mark with a picture of a folder.

i know i've got to hold down the "C" key when using the tiger install disk, but again nothing happens.

I tried using Target Disk Mode with my new MacBook Pro, and again, it doesn't work. I hold down the T key and start it up under Target Disk Mode and nothing happens.

So my question to you all ... does anybody know if Target Disk Mode is build-in to the hardware or is it part of the software. For example, if you stick in a unformatted hard-drive with nothing on it into your old powerbook, can you still access that via Target Disk Mode via a new MacBook Pro?

I'm just wondering if I perhaps made a mistake reconnecting the keyboard ribbon, which might explain why nothing happens when I press the "C" or "T" buttons on start-up?

Thanks in advance for any help!