As the most of you have probably noticed the SQL Server 2008 RTM is released last week. This means that we can actually use PowerPivot as a finished product, download it here
To give you a quick startup on PowerPivot i created a post that contains a lot of information on PowerPivot collected from my blog, check it out here: http://www.kasperonbi.com/getting-started-with-powerpivot