This guide was originally created by the brilliant Shara. Nowdays Mira maintain / update it as well as having a HTML version of it available.
The Excel file is recommended, with a lot more viewing options and functions that work as they should. For instance being able to zoom out to easier get an overview of all data. For a free Excel file viewing program from Microsoft click here. Alternatively, OpenOffice is a free office suite with a Calc program that can view .xls files.