Below is the MSDN Blog I read it from; below that is the excerpt from the blog if you don't want to go to it.
http://blogs.msdn.com/robertbrown/archive/2009/02/20/sp2-has-been-updated-to-support-speech-barge-in.aspx
Microsoft has listened and updated SP2 to include Barge-In on AA.
To install it....
Rather than supply a separate patch that would need to be applied every time you installed SP2, we've slip-streamed the fix directly into SP2.
1. Download the current
http://www.microsoft.com/downloads/details.aspx?FamilyID=5cb5dfc0-cc00-4446-b087-455322d04003&displaylang=en and unzip it. (If you've downloaded SP2 prior to today, just download it again to pick up the optional barge-in functionality)
2. Install the Administrator software on your workstation.
3. When you log in to Administrator, it will prompt you to upgrade the base unit. When you're done, your base unit software version should be 1.21.5017.0
Dustin