need to STOP that lion in it's tracks right there. Just select "Quit" from the "File" menu. Then, go into your "Applications" folder and copy the Mountain Lion Installer to another location like your Desktop. (Remember to copy and not move.) You can see that the installer is about 4.37 GB (as I mentioned before, the expanded size is LARGER than what will fit on a single-sided DVD so get a dual-sided DVD). Step Three -- Show Package Contents & Copy the Installer File From the copy that you created of the installer (e.g., the one on your Desktop), you will need to extract the actual installer DMG from the Package Contents. To do this, right-click on the Installer file and choose "Show Package Contents". From within the Package Contents, navigate to: Contents &gt; Shared Support and select the "InstallESD.dmg" file and COPY that back to your Desktop (or wherever you want). You will need this file ("InstallESD.dmg") for the bootable DVD. Remember the location where you put that .dmg file. Step Four -- Burn the DVD (or the USB drive) The next step is to burn the actual DVD. As I already said a few times, you need a dual-sided DVD (see step 4a below on how to burn a single-sided DVD). I only had a single-sided DVD so I'm showing the steps here that you would use. (Note: untested instructions for how to make a bootable USB thumb drive are below as well.) If you new image/partition doesn't