Step 1: Open Up
First we'll have to locate all the screws: a couple of them will be sealed away under white or "warranty void if removed" stickers.
Find 'em and remove all of them.
Open up, you might need to pry it open with a flat screwdriver, since many HDD producers use some kind of gummy stuff to keep the HDDs airtight.
Step 2: Strip It Down
let's begin by prying off the upper support for the heads mount.
Now, pushing with your finger on the copper coil you just exposed slide the heads off the disk[s] and unscrew the bearing with a large flat screwdriver. They'll come rigt off, but you'll notice that they still hang to the HDD body by a flat wire.
Unscrew the evntual screws keeping the flat connector down and pull hard to remove.
Unscreew the rare earth magnet and store it for future projects.
Unscrew the 3 screws that keep the disk attached to the motor, and set aside along with the small disk, then lift off the main disk.
Step 3: Add the Disk
Step 4: Power On
I used an adapter that I had lying around in my wiring drawer, but you can also power it up by shorting the green wire with a black wire on an ATX power supply.