Microsoft® PowerPivot for Microsoft® Excel 2010 provides ground-breaking technology, such as fast manipulation of large data sets (often millions of rows), streamlined integration of data, and the ability to effortlessly share your analysis through Microsoft® SharePoint 2010.

Microsoft® PowerPivot for Microsoft® Excel 2010 is a data analysis tool that delivers unmatched computational power directly within the software users already know and love — Microsoft® Excel. You can transform mass quantities of data with incredible speed into meaningful information to get the answers you need in seconds. You can effortlessly share your findings with others.

This video from the Microsoft PowerPivot website gives an overview of PowerPivot and the installation of the PowerPivot Add-In for Excel 2010. Essentially you download the 81.7MB file, install the add-in, open Excel 2010 and click on the PowerPivot tab on the ribbon which will then launch the PowerPivot window.