XLSX files are the default spreadsheet file format for Excel 2007. This particular file format is the XML based file format that was created specifically for the release of Microsoft Office 2007. Until recently the file format was exclusive only to Microsoft Office 2007, however Microsoft released a compatibility pack that allowed Microsoft Office 2007 and Office 2003 to interface. This converter can be used even if Office 2003 is not installed. OpenOffice, a free program from Sun Microsystems, can be used with this file converter to open xlsx files.
In order to open xlsx files, simply download and install OpenOffice first. Then download and install the newest version of the Microsoft Office Compatibility pack from Microsoft. If Microsoft Office 2003 is installed then your computer will open xlsx files with Excel. If not, the program to open xlsx files will be OpenOffice Calc (the OpenOffice equivalent of Excel). If your system does not default to either of these, you can open xlsx files by starting OpenOffice Calc, then clicking the “File” button on the top bar, then “Open” and then selecting the xlsx file you would like to open. This method is a free alternative to open xlsx files without having to purchase Microsoft Office 2007.