how to download os x before reinstalling

Assuming you purchased Lion (10.7.5) from the App Store, you can open the App Store, press/hold the Option/Alt key and click on the Purchases tab. From there you should see Lion in your purchases and download it. After the download completes and you're presented with a screen to Continue, do not press continue. Right click the Install OS X icon on your Dock and Quit out of it. Now, locate the OS X Install app in your applications folder and follow this link's instructions on extracting the InstallESD.dmg file and putting it on a USB thumb drive (8GB).

Are you holding down the Option key while clicking on Purchases? Assuming again, that you purchased Lion from the Apps Store with your Apple ID, you should see the Lion icon on the left side of the Purchases screen with the Download button ungreyed.

If your system came preinstalled with Lion, then it's a different procedure.

If your system came with the version of OS X you are trying to install, then you will not be able to create a boot drive from it. You will need to boot to the OS X Recovery HD partition by holding Command-R at startup (or to Internet Recovery by holding Option-Command-R), after which OS X 10.7 will download from the App Store when your system logs in and is recognized as having been originally shipped with 10.7. Technically the installer files do download to your system, but you will not have access to them so you cannot create a separate boot drive from them. The only way to do this is if you have purchased OS X from the App Store, where you can then download it to your system and extract the installation files.

The best way is to:

Plug in a USB external drive

Restart into Internet Recovery using the Command+Option+R keys. This boots into Apple's servers and their Recovery HD so you can download the specific version of Lion for your Mac.

Select Install or Reinstall OS X from the OS X Utilities Menu. Point to your external USB drive to install on.

IMPORTANT: You will need to pay attention to the download. After it finishes and when your Mac restarts. At the black screen, unplug your external USB drive and your Mac will boot to your normal Desktop.

Plug your USB external drive in and navigate to the OS X Install Data folder and extract the InstallESD.dmg file. Copy this file to your Desktop.

Using a bootable (Mac OS X Extended-Journaled - GUID partition table) USB 8GB thumb drive, open Disk Utility, select the USB thumb drive and click on the Restore tab. Select your Source file as the InstallESD.dmg file on your desktop. Select your USB thumb drive as your Destination. Click the Restore button. This will create a bootable USB thumb drive with the Lion installer so you can boot from it and install Lion.

Ah, good approach. 🙂

Holding down the option key while clicking the purchases tab doesn't allow me to download items that show as installed?????

gurdulu wrote:

The last question before I try is: once the download has finished, does your mac prompt you to restart, or do you have to take a look at your screen now and then and when it's like 97% done, get ready to jump on your external drive to unplug it otherwise it's too late?...

You have to watch it as you will not be prompted to continue. That's why I put IMPORTANT and bolded that step. If you let it restart before unplugging the external drive, it's too late.

Eric Root wrote:

Holding down the option key while clicking the purchases tab doesn't allow me to download items that show as installed?????

His Mac came preinstalled with Lion.