Thank you for the guide. My 2008 24 inch imac has been use as a paperweight for the past 4 years after the HD failed. I replaced it with a 27 inch imac, but I decided to have go at fixing the old one. I replaced the 320 WD HD with a WD 2 TB today. All went well until trying to reinstall the original OS (Snow Leopard) and could not get the computer to see the new HD. Your guide saved the day and now have the OS installed. Thanks again.