If you followed my earlier post (http://blogs.msdn.com/b/querysimon/archive/2011/07/18/installing-sharepoint-2010-together-with-denali-ctp3.aspx) about installing Denali CTP3 together with SharePoint 2010 then you will find that Reporting Services have not been enabled in the SharePoint site. One thing that has changed in Denali compared to SQL Server 2008 R2 is that Reporting Services is a shared service when it is installed in SharePoint integrated mode.
If you installed SharePoint 2010 after you installed SQL Server Denali then the installation was not able to configure the integration. Solution to this is to either follow the blog post that Pej posted here on installation order http://blogs.msdn.com/b/oneclickbi/archive/2011/07/21/getting-up-and-running-with-sql-server-denali-for-business-intelligence-crescent-and-powerpivot-in-ctp3.aspx
Or you can enable it later by following the documentation running some PowerShell scripts to enable it afterwards.
You can find the PowerShell commands that need to be executed in Books Online at the following link http://msdn.microsoft.com/en-us/library/gg492276(v=SQL.110).aspx
You need to follow the sections about Install and Start the Reporting Services SharePoint Service and Create a Reporting Services Service Application.
After this you should be able to use Crescent in SharePoint 2010.