How to Correctly Install Power Pivot for Excel 2010

As most subscribers of my blog would already know, I am a professional trainer of Power Pivot here in Australia. I do a lot of work for Corporations at their own premises with their own PC equipment. Not every company has made the move to Excel 2013, and in fact I sometimes find companies have to move from Excel 2007 to 2010 just to prepare for this training. There are a couple of traps when installing the Power Pivot for Excel 2010 Plug-in (and the Power Query Plug-in for that matter) and hence I am blogging these instructions to help people and companies get it right the first time. The main trap is getting the wrong version. But first a comment about 32 bit vs 64 bit.