Download instructions and links to download locations for different flavours of Powerpivot can be accessed from here.
Those who are not able to download and install Powerpivot (as it also requires installation of Office 2010 beta in one or another way), need not to get disappointed. A Virtual Lab of Powerpivot for Excel 2010 Introduction is available from Microsoft. Aspirants can use this lab, and get their hands-on this lab to get the feel of Powerpivot without bothering about any download or installation.
This Virtual Lab can be accessed from here.