Copy your most important stuff to a CD or floppies.
Once you have done this, remove the HD.
When you have the HD out, place it on a solid surface and using a 1kg hammer, procede to smash it flat.
Continue to smash the old HD flat until you have it flat enough to fit into a mail slot.
Buy another HD.
Install.
Copy your important stuff to your new HD.
If you follow these instructions, you will be VERY happy!!!!!!!!!