Currently Being ModeratedMar 15, 2013 6:38 AM (in response to Lamija)
If you lost your install disk, you will need something to use to install Mac OS X on a new hard drive. Apple no longer carries the retail version of Leopard, you might try calling 1-800-MY-APPLE and see if they can send a machine-specific disk to you, for a fee of course. Otherwise search Amazon, eBay or the like for Leopard.
You could also consider buying the Snow Leopard install disk from the Apple on-line store ($20) to use to install 10.6 on a new hard drive.