Delphi Prism 2010 running in the Visual Studio 2010 is in the works.
Here's an early demo of it earlier this year at Delphi Live!
Visual Studio 2010 support didn't make it into the Delphi Prism 2010 August 2009 release but it's planned to be in the next rev of Delphi Prism 2010 later this fall according to posts from the developers.
All Delphi Prism and RAD Studio users with current maintenance will get it when it's available. That's a good reason to keep current with your maintenance because new feature releases are only available to users on maintenance.