MacPostfactor is a tool to install Mac OSX 10.8+ on older Macbooks that normally only support up to OSX 10.7 (Lion). It works through a combination of a highly customized installer, a replaced set of drivers and various frameworks, and the original installation app from the App Store. The installation can be done directly on a Macbook already running OSX Lion (so no USB disk required), or on an USB media for installation on another system.
No particular or in-depth knowledge of Mac or OSX is required to use this. The installation can be done directly on a working Mac that's running OSX Lion (10.7).
Using MacPostFactor is very straight forward:
The only tricky part is to actually get the install app from the App Store of the OSX version you want to install. The App Store does not allow you to download the app on a Macbook that does not support it, so you'll have to be a bit creative.
You could use a Mac that supports the newer OSX versions and directly download the app from the App Store that way. It is not a problem if the OSX on that Mac is newer than the version you want to download. You'll get a warning but the download will continue. Once downloaded, you can then copy the app from the /Applications folder to another system, through network or USB.
If you use an USB media, it's best to "compress" the app before copying to ensure all files remain in place: right-click the app, then click Compress. This will create a ZIP file in the current folder.