Drive Preparation and Installation
1. Boot from your Snow Leopard Installer Disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu.
2. After DU loads select your hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Note the SMART status of the drive in DU's status area. If it does not say "Verified" then the drive is failing or has failed and will need replacing. SMART info will not be reported on external drives. Otherwise, click on the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed.
4. Select the volume you just created (this is the sub-entry under the drive entry) from the left side list. Click on the Erase tab in the DU main window.
5. Set the format type to Mac OS Extended (Journaled.) Click on the Security button, check the button for Zero Data and click on OK to return to the Erase window.
6. Click on the Erase button. The format process can take up to several hours depending upon the drive size.
7. After formatting is completed quit DU and return to the installer. Install Snow Leopard.
Yes, but before you do that would you please tell us exactly which model you have. Some models cannot boot from the retail disc because they require a later version only available on the original discs that came with the computer. You should have received those discs from the seller.
Let's first be sure if you can start the computer from a retail disc before you spend money on it. You may find it preferable to buy the Apple USB Lion Flash Drive installer at your local Apple retailer - $69.00 - and just go ahead and install Lion.
I did not realize that you had no installer discs for your computer, so that complicates things just a little bit.