Thanks to hackerwayne for the tip, and for creating MLPostFactor! It won’t be running a new OS, but at least it’ll be a bit quicker. If your older Mac doesn’t fit the compatibility list, don’t feel too bad, but try out some tips to speed it up instead to breathe some new life into it. If you meet the requirements, you’ll need to download the MLPostFactor app ( link here), re-download Mountain Lion from the App Store, and, ideally, create a installer drive as if you were going to perform a clean install on a regular compatible Mac. Do note that some of the older Mac Pro and Xserve models have specific GPU requirements as well, so be sure to read the full MLPostFactor tutorial before beginning in order to determine if there is anything incompatible with the specific Mac model you are looking to install this on. The requirements are basically such that if it supports Lion, it will now support Mountain Lion.

Mac released from 2006 to 2008 with Core 2 Duo CPU and Lion installed – PPC, Core Duo, and Core Solo chips are not supported.

How to upgrade macbook pro os x 10.5.8