A long time Groove partner provides guidance on moving your data directory.
Every now and again the question comes up -- hey, how do I move my data directory? The official answer from the team is "you can't -- we only support the default installation". However, there's an unofficial answer too, and Kevin Reeuwijk from Getronics provides it here.
Link to this article: http://blogs.technet.com/groove/archive/2007/05/30/how-to-move-your-data-files.aspx